diff --git a/tianshou/env/utils.py b/tianshou/env/utils.py
index ac67101..cbd36d9 100644
--- a/tianshou/env/utils.py
+++ b/tianshou/env/utils.py
@@ -4,7 +4,10 @@ import cloudpickle
 import gymnasium
 import numpy as np
 
-from tianshou.env.pettingzoo_env import PettingZooEnv
+try:
+    from tianshou.env.pettingzoo_env import PettingZooEnv
+except ImportError:
+    PettingZooEnv = None  # type: ignore
 
 if TYPE_CHECKING:
     import gym