diff --git a/packages/proto-plus/docs/fields.rst b/packages/proto-plus/docs/fields.rst
index 1961cff07407..e85934944dc6 100644
--- a/packages/proto-plus/docs/fields.rst
+++ b/packages/proto-plus/docs/fields.rst
@@ -81,7 +81,7 @@ Declare them in Python using the :class:`~.RepeatedField` class:
         >>> row.values = [struct_pb2.Value(string_value="hello")]
         Traceback (most recent call last):
         File "<stdin>", line 1, in <module>
-        File "/usr/local/google/home/busunkim/github/python-automl/.nox/unit-3-8/lib/python3.8/site-packages/proto/message.py", line 543, in __setattr__
+        File "/usr/local/google/home/busunkim/github/python-automl/.nox/unit-3-10/lib/python3.10/site-packages/proto/message.py", line 543, in __setattr__
             self._pb.MergeFrom(self._meta.pb(**{key: pb_value}))
         TypeError: Value must be iterable
 
diff --git a/packages/proto-plus/noxfile.py b/packages/proto-plus/noxfile.py
index 1cf600b1b1b1..265dc22711ea 100644
--- a/packages/proto-plus/noxfile.py
+++ b/packages/proto-plus/noxfile.py
@@ -30,7 +30,6 @@
 DEFAULT_PYTHON_VERSION = "3.14"
 
 PYTHON_VERSIONS = [
-    "3.9",
     "3.10",
     "3.11",
     "3.12",
diff --git a/packages/proto-plus/proto/enums.py b/packages/proto-plus/proto/enums.py
index d3ab6b792023..6ddf63a2cce5 100644
--- a/packages/proto-plus/proto/enums.py
+++ b/packages/proto-plus/proto/enums.py
@@ -55,8 +55,7 @@ def __new__(mcls, name, bases, attrs):
         opts = attrs.pop(pb_options, {})
         # This is the only portable way to remove the _pb_options name
         # from the enum attrs.
-        # In 3.7 onwards, we can define an _ignore_ attribute and do some
-        # mucking around with that.
+        # TODO: Use _ignore_ attribute to ignore _pb_options (Issue #16911)
         if pb_options in attrs._member_names:
             if isinstance(attrs._member_names, list):
                 idx = attrs._member_names.index(pb_options)
diff --git a/packages/proto-plus/proto/marshal/collections/repeated.py b/packages/proto-plus/proto/marshal/collections/repeated.py
index a6560411cd71..3ce3923f6dc8 100644
--- a/packages/proto-plus/proto/marshal/collections/repeated.py
+++ b/packages/proto-plus/proto/marshal/collections/repeated.py
@@ -166,10 +166,10 @@ def __setitem__(self, key, value):
             else:  # Is an extended slice.
                 indices = range(start, stop, step)
 
-                if len(value) != len(indices):  # XXX: Use PEP 572 on 3.8+
+                if (v_len := len(value)) != len(indices):
                     raise ValueError(
                         f"attempt to assign sequence of size "
-                        f"{len(value)} to extended slice of size "
+                        f"{v_len} to extended slice of size "
                         f"{len(indices)}"
                     )
 
diff --git a/packages/proto-plus/pyproject.toml b/packages/proto-plus/pyproject.toml
index 568db53e0d2d..efe9a2a3b2ec 100644
--- a/packages/proto-plus/pyproject.toml
+++ b/packages/proto-plus/pyproject.toml
@@ -20,7 +20,7 @@ build-backend = "setuptools.build_meta"
 name = "proto-plus"
 authors = [{ name = "Google LLC", email = "googleapis-packages@google.com" }]
 license = { text = "Apache 2.0" }
-requires-python = ">=3.9"
+requires-python = ">=3.10"
 description = "Beautiful, Pythonic protocol buffers"
 readme = "README.rst"
 classifiers = [
@@ -29,7 +29,6 @@ classifiers = [
   "License :: OSI Approved :: Apache Software License",
   "Programming Language :: Python",
   "Programming Language :: Python :: 3",
-  "Programming Language :: Python :: 3.9",
   "Programming Language :: Python :: 3.10",
   "Programming Language :: Python :: 3.11",
   "Programming Language :: Python :: 3.12",