diff --git a/.github/workflows/build-release.yml b/.github/workflows/build-release.yml
index 1ab2f89..bcfb90f 100644
--- a/.github/workflows/build-release.yml
+++ b/.github/workflows/build-release.yml
@@ -16,10 +16,8 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - { name: "3.10-ma3", tox: py310-marshmallow3 }
-          - { name: "3.14-ma3", tox: py314-marshmallow3 }
-          - { name: "3.10-ma4", tox: py310-marshmallow4 }
-          - { name: "3.14-ma4", tox: py314-marshmallow4 }
+          - { name: "3.10", tox: py310 }
+          - { name: "3.14", tox: py314 }
           - { name: "lowest", tox: py310-lowest }
           - { name: "dev", tox: py314-marshmallowdev }
     steps:
diff --git a/CHANGELOG.rst b/CHANGELOG.rst
index 47cc3c0..29cee12 100644
--- a/CHANGELOG.rst
+++ b/CHANGELOG.rst
@@ -7,6 +7,7 @@ unreleased
 Support:
 
 - Support Python 3.10-3.14.
+- Drop support for marshmallow 3, which is EOL.
 
 3.2.0 (2025-05-08)
 ******************
diff --git a/pyproject.toml b/pyproject.toml
index 4c2f47c..eaf8978 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -16,7 +16,7 @@ classifiers = [
   "Programming Language :: Python :: 3.14",
 ]
 requires-python = ">=3.10"
-dependencies = ["marshmallow>=3.0.0,<5.0.0"]
+dependencies = ["marshmallow>=4.0.0,<5.0.0"]
 
 [project.urls]
 Issues = "https://github.com/marshmallow-code/marshmallow-oneofschema/issues"
diff --git a/tox.ini b/tox.ini
index eead224..62bd3fb 100644
--- a/tox.ini
+++ b/tox.ini
@@ -1,18 +1,15 @@
 [tox]
 envlist=
     lint
-    py{310,314}-marshmallow3
-    py{310,311,312,313,314}-marshmallow4
+    py{310,311,312,313,314}
     py314-marshmallowdev
     py310-lowest
 
 [testenv]
 dependency_groups = tests
 deps =
-    marshmallow3: marshmallow>=3.0.0,<4.0.0
-    marshmallow4: marshmallow>=4.0.0,<5.0.0
     marshmallowdev: https://github.com/marshmallow-code/marshmallow/archive/dev.tar.gz
-    lowest: marshmallow==3.0.0
+    lowest: marshmallow==4.0.0
 commands = pytest {posargs}
 
 [testenv:lint]
diff --git a/uv.lock b/uv.lock
index 09ee301..0cd3de0 100644
--- a/uv.lock
+++ b/uv.lock
@@ -144,7 +144,7 @@ tests = [
 ]
 
 [package.metadata]
-requires-dist = [{ name = "marshmallow", specifier = ">=3.0.0,<5.0.0" }]
+requires-dist = [{ name = "marshmallow", specifier = ">=4.0.0,<5.0.0" }]
 
 [package.metadata.requires-dev]
 dev = [