diff --git a/sdk/servicebus/azure-servicebus/CHANGELOG.md b/sdk/servicebus/azure-servicebus/CHANGELOG.md
index 1fdc4a3f450a..7a37a5ee9c76 100644
--- a/sdk/servicebus/azure-servicebus/CHANGELOG.md
+++ b/sdk/servicebus/azure-servicebus/CHANGELOG.md
@@ -14,6 +14,7 @@
 - Fixed a bug where the async receiver factory methods on `azure.servicebus.aio.ServiceBusClient` (`get_queue_receiver`, `get_subscription_receiver`) and the async `ServiceBusReceiver` annotated the `auto_lock_renewer` keyword with the synchronous `AutoLockRenewer`, causing static type checkers to reject the documented `azure.servicebus.aio.AutoLockRenewer` usage. The annotation now references the async `AutoLockRenewer`, matching the docstrings and runtime behavior. ([#47948](https://github.com/Azure/azure-sdk-for-python/issues/47948))
 - Fixed a bug where closing a `PEEK_LOCK` receiver did not release messages that had been prefetched into the client buffer or were still in flight, so they remained locked at the broker until lock expiry — delaying their redelivery and inflating their delivery count. On close, a non-session `PEEK_LOCK` receiver now drains the link (stopping the broker and flushing in-flight transfers) and releases the buffered messages (`released` disposition), so the broker can redeliver them immediately without incrementing the delivery count. ([#42917](https://github.com/Azure/azure-sdk-for-python/issues/42917))
 - Fixed a bug where the async pure-Python AMQP transport failed to connect with `[Errno 22] Invalid argument` (`amqp:socket-error`) inside containerized/virtualized environments such as Docker Desktop on macOS. The transport no longer reads back and re-applies platform-negotiated TCP options (e.g. `TCP_MAXSEG`) that some platforms reject via `setsockopt`. ([#45394](https://github.com/Azure/azure-sdk-for-python/issues/45394))
+- Fixed a bug where passing a `fully_qualified_namespace` that included a port and/or trailing path (for example the `https://<namespace>.servicebus.windows.net:443/` form that Azure returns when provisioning a namespace) raised `ServiceBusAuthenticationError`. The namespace is now normalized to its bare host, matching the .NET and JavaScript SDKs. ([#44034](https://github.com/Azure/azure-sdk-for-python/issues/44034))
 
 ### Other Changes
 
diff --git a/sdk/servicebus/azure-servicebus/azure/servicebus/_base_handler.py b/sdk/servicebus/azure-servicebus/azure/servicebus/_base_handler.py
index 642597b7702b..31ad3df26f72 100644
--- a/sdk/servicebus/azure-servicebus/azure/servicebus/_base_handler.py
+++ b/sdk/servicebus/azure-servicebus/azure/servicebus/_base_handler.py
@@ -252,8 +252,10 @@ def __init__(
     ) -> None:
         self._amqp_transport = kwargs.pop("amqp_transport", PyamqpTransport)
 
-        # If the user provided http:// or sb://, let's be polite and strip that.
-        self.fully_qualified_namespace: str = strip_protocol_from_uri(fully_qualified_namespace.strip())
+        # Keep the port for the non-TLS emulator; strip scheme/port/path otherwise.
+        self.fully_qualified_namespace: str = strip_protocol_from_uri(
+            fully_qualified_namespace.strip(), strip_port=kwargs.get("use_tls", True)
+        )
         self._entity_name = entity_name
 
         subscription_name = kwargs.get("subscription_name")
diff --git a/sdk/servicebus/azure-servicebus/azure/servicebus/_common/utils.py b/sdk/servicebus/azure-servicebus/azure/servicebus/_common/utils.py
index ebc6b4452852..92f6f9e981fc 100644
--- a/sdk/servicebus/azure-servicebus/azure/servicebus/_common/utils.py
+++ b/sdk/servicebus/azure-servicebus/azure/servicebus/_common/utils.py
@@ -245,15 +245,37 @@ def transform_outbound_messages(
     return _convert_to_single_service_bus_message(messages, message_type, to_outgoing_amqp_message)
 
 
-def strip_protocol_from_uri(uri: str) -> str:
-    """Removes the protocol (e.g. http:// or sb://) from a URI, such as the FQDN.
+def strip_protocol_from_uri(uri: str, *, strip_port: bool = True) -> str:
+    """Reduce a URI to its bare host by removing the scheme (e.g. sb://) and path.
+
+    The port is also removed by default (e.g. the ``:443/`` in the ARM-emitted
+    ``https://<ns>.servicebus.windows.net:443/``). Pass ``strip_port=False`` for
+    the development emulator, whose non-default port must be kept.
+
     :param str uri: The URI to modify.
-    :return: The URI without the protocol.
+    :keyword bool strip_port: Whether to also remove a trailing port. Defaults to ``True``.
+    :return: The bare host portion of the URI.
     :rtype: str
     """
+    # Strip the scheme (everything up to and including "//").
     left_slash_pos = uri.find("//")
     if left_slash_pos != -1:
-        return uri[left_slash_pos + 2 :]
+        uri = uri[left_slash_pos + 2 :]
+    # Strip the path (the first "/" and everything after it).
+    slash_pos = uri.find("/")
+    if slash_pos != -1:
+        uri = uri[:slash_pos]
+    if not strip_port:
+        return uri
+    # Strip the port, but preserve a bracketed IPv6 literal (e.g. "[fe80::1]").
+    if uri.startswith("["):
+        bracket_pos = uri.find("]")
+        if bracket_pos != -1:
+            uri = uri[: bracket_pos + 1]
+    else:
+        colon_pos = uri.find(":")
+        if colon_pos != -1:
+            uri = uri[:colon_pos]
     return uri
 
 
diff --git a/sdk/servicebus/azure-servicebus/azure/servicebus/_servicebus_client.py b/sdk/servicebus/azure-servicebus/azure/servicebus/_servicebus_client.py
index 86a0be498e3c..fb7a4b202689 100644
--- a/sdk/servicebus/azure-servicebus/azure/servicebus/_servicebus_client.py
+++ b/sdk/servicebus/azure-servicebus/azure/servicebus/_servicebus_client.py
@@ -138,8 +138,10 @@ def __init__(
 
         self._amqp_transport = amqp_transport
 
-        # If the user provided http:// or sb://, let's be polite and strip that.
-        self.fully_qualified_namespace: str = strip_protocol_from_uri(fully_qualified_namespace.strip())
+        # Keep the port for the non-TLS emulator; strip scheme/port/path otherwise.
+        self.fully_qualified_namespace: str = strip_protocol_from_uri(
+            fully_qualified_namespace.strip(), strip_port=kwargs.get("use_tls", True)
+        )
 
         self._credential = credential
         # TODO: can we remove this here? it's recreated in Sender/Receiver
diff --git a/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_base_handler_async.py b/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_base_handler_async.py
index c97787ccb801..bde1a82d6771 100644
--- a/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_base_handler_async.py
+++ b/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_base_handler_async.py
@@ -131,8 +131,10 @@ def __init__(
     ) -> None:
         self._amqp_transport = kwargs.pop("amqp_transport", PyamqpTransportAsync)
 
-        # If the user provided http:// or sb://, let's be polite and strip that.
-        self.fully_qualified_namespace: str = strip_protocol_from_uri(fully_qualified_namespace.strip())
+        # Keep the port for the non-TLS emulator; strip scheme/port/path otherwise.
+        self.fully_qualified_namespace: str = strip_protocol_from_uri(
+            fully_qualified_namespace.strip(), strip_port=kwargs.get("use_tls", True)
+        )
         self._entity_name = entity_name
 
         subscription_name = kwargs.get("subscription_name")
diff --git a/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_servicebus_client_async.py b/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_servicebus_client_async.py
index b0387f27e4c3..1af5e1d28084 100644
--- a/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_servicebus_client_async.py
+++ b/sdk/servicebus/azure-servicebus/azure/servicebus/aio/_servicebus_client_async.py
@@ -130,8 +130,10 @@ def __init__(
                 raise ValueError("To use the uAMQP transport, please install `uamqp>=1.6.3,<2.0.0`.") from None
 
         self._amqp_transport = amqp_transport
-        # If the user provided http:// or sb://, let's be polite and strip that.
-        self.fully_qualified_namespace: str = strip_protocol_from_uri(fully_qualified_namespace.strip())
+        # Keep the port for the non-TLS emulator; strip scheme/port/path otherwise.
+        self.fully_qualified_namespace: str = strip_protocol_from_uri(
+            fully_qualified_namespace.strip(), strip_port=kwargs.get("use_tls", True)
+        )
         self._credential = credential
         self._config = Configuration(
             retry_total=retry_total,
diff --git a/sdk/servicebus/azure-servicebus/tests/test_connection_string_parser.py b/sdk/servicebus/azure-servicebus/tests/test_connection_string_parser.py
index 956a67eaccfc..c56e07cf382e 100644
--- a/sdk/servicebus/azure-servicebus/tests/test_connection_string_parser.py
+++ b/sdk/servicebus/azure-servicebus/tests/test_connection_string_parser.py
@@ -7,14 +7,23 @@
 import os
 import pytest
 from azure.servicebus import (
+    ServiceBusClient,
     ServiceBusConnectionStringProperties,
     parse_connection_string,
 )
+from azure.servicebus.aio import ServiceBusClient as ServiceBusClientAsync
+from azure.servicebus._common.utils import strip_protocol_from_uri
 
 from devtools_testutils import AzureMgmtRecordedTestCase
 
 
-class ServiceBusConnectionStringParserTests(AzureMgmtRecordedTestCase):
+_EMULATOR_CONN_STR = (
+    "Endpoint=sb://localhost:5673;SharedAccessKeyName=RootManageSharedAccessKey;"
+    "SharedAccessKey=SAS_KEY_VALUE;UseDevelopmentEmulator=true;"
+)
+
+
+class TestServiceBusConnectionStringParser(AzureMgmtRecordedTestCase):
     def test_sb_conn_str_parse_cs(self, **kwargs):
         conn_str = "Endpoint=sb://resourcename.servicebus.windows.net/;SharedAccessKeyName=test;SharedAccessKey=THISISATESTKEYXXXXXXXXXXXXXXXXXXXXXXXXXXXX="
         parse_result = parse_connection_string(conn_str)
@@ -103,7 +112,7 @@ def test_sb_parse_malformed_conn_str_lowercase_sa_key_name(self, **kwargs):
             parse_result = parse_connection_string(conn_str)
         assert str(e.value) == "Connection string must have both SharedAccessKeyName and SharedAccessKey."
 
-    def test_sb_parse_malformed_conn_str_lowercase_sa_key_name(self, **kwargs):
+    def test_sb_parse_malformed_conn_str_lowercase_sa_key(self, **kwargs):
         conn_str = "Endpoint=sb://resourcename.servicebus.windows.net/;SharedAccessKeyName=test;sharedaccesskey=THISISATESTKEYXXXXXXXXXXXXXXXXXXXXXXXXXXXX="
         with pytest.raises(ValueError) as e:
             parse_result = parse_connection_string(conn_str)
@@ -112,15 +121,45 @@ def test_sb_parse_malformed_conn_str_lowercase_sa_key_name(self, **kwargs):
     def test_sb_parse_emulator_string(self, **kwargs):
         conn_str = "Endpoint=sb://localhost;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=SAS_KEY_VALUE;UseDevelopmentEmulator=true;"
         parse_result = parse_connection_string(conn_str)
-        assert parse_result.endpoint == "sb://localhost"
+        assert parse_result.endpoint == "sb://localhost/"
         assert parse_result.fully_qualified_namespace == "localhost"
 
         conn_str = "Endpoint=sb://servicebus-emulator;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=SAS_KEY_VALUE;UseDevelopmentEmulator=true;"
         parse_result = parse_connection_string(conn_str)
-        assert parse_result.endpoint == "sb://servicebus-emulator"
+        assert parse_result.endpoint == "sb://servicebus-emulator/"
         assert parse_result.fully_qualified_namespace == "servicebus-emulator"
 
         conn_str = "Endpoint=sb://192.168.y.z;SharedAccessKeyName=RootManageSharedAccessKey;SharedAccessKey=SAS_KEY_VALUE;UseDevelopmentEmulator=true;"
         parse_result = parse_connection_string(conn_str)
-        assert parse_result.endpoint == "sb://192.168.y.z"
-        assert parse_result.fully_qualified_namespace == "192.168.y.z"
\ No newline at end of file
+        assert parse_result.endpoint == "sb://192.168.y.z/"
+        assert parse_result.fully_qualified_namespace == "192.168.y.z"
+
+    def test_strip_protocol_from_uri_normalizes_to_bare_host(self, **kwargs):
+        # regression test for issue #44034: scheme, port and trailing path are
+        # stripped so the ARM-emitted https://<ns>...:443/ form yields a bare host
+        host = "myservicebus.servicebus.windows.net"
+        assert strip_protocol_from_uri(host) == host  # bare host (known-good)
+        assert strip_protocol_from_uri("sb://" + host) == host  # protocol only
+        assert strip_protocol_from_uri("https://" + host) == host
+        assert strip_protocol_from_uri("http://" + host) == host
+        assert strip_protocol_from_uri("sb://" + host + "/") == host  # trailing slash
+        assert strip_protocol_from_uri(host + ":443") == host  # port only (no scheme)
+        assert strip_protocol_from_uri(host + ":443/") == host
+        assert strip_protocol_from_uri("https://" + host + ":443/") == host  # ARM/portal-emitted form
+        assert strip_protocol_from_uri("sb://" + host + ":5671/") == host
+
+        # bracketed IPv6 literals are preserved; only a port after "]" is stripped
+        assert strip_protocol_from_uri("[fe80::1]") == "[fe80::1]"
+        assert strip_protocol_from_uri("[fe80::1]:5671") == "[fe80::1]"
+        assert strip_protocol_from_uri("sb://[fe80::1]:5671/") == "[fe80::1]"
+
+    def test_emulator_nondefault_port_preserved_sync(self, **kwargs):
+        client = ServiceBusClient.from_connection_string(_EMULATOR_CONN_STR)
+        try:
+            assert client.fully_qualified_namespace == "localhost:5673"
+        finally:
+            client.close()
+
+    def test_emulator_nondefault_port_preserved_async(self, **kwargs):
+        client = ServiceBusClientAsync.from_connection_string(_EMULATOR_CONN_STR)
+        assert client.fully_qualified_namespace == "localhost:5673"