diff --git a/gymnasium/envs/mujoco/mujoco_env.py b/gymnasium/envs/mujoco/mujoco_env.py
index 1c1a986fe..956fda093 100644
--- a/gymnasium/envs/mujoco/mujoco_env.py
+++ b/gymnasium/envs/mujoco/mujoco_env.py
@@ -329,6 +329,7 @@ def _get_viewer(
 
     def close(self):
         if self.viewer is not None:
+            self.viewer.free()
             self.viewer = None
             self._viewers = {}