diff --git a/alf/algorithms/config.py b/alf/algorithms/config.py
index 2b8f94e4e..9f2a3dc37 100644
--- a/alf/algorithms/config.py
+++ b/alf/algorithms/config.py
@@ -53,6 +53,7 @@ def __init__(self,
                  num_eval_episodes=10,
                  num_eval_environments: int = 1,
                  async_eval: bool = True,
+                 shared_train_eval_env: bool = False,
                  save_checkpoint_for_best_eval: Optional[Callable] = None,
                  ddp_paras_check_interval: int = 0,
                  num_summaries=None,
@@ -227,6 +228,10 @@ def __init__(self,
             num_eval_environments: the number of environments for evaluation.
             async_eval: whether to do evaluation asynchronously in a different
                 process. Note that this may use more memory.
+            shared_train_eval_env: whether the training and evaluation environments are
+                shared. If True, the environment instance used in training will also be
+                used in evaluation. This is useful for cases such as rl-in-real with a
+                single physical environment.
             save_checkpoint_for_best_eval: If provided, will be called with a list of
                 evaluation metrics. If it returns True, a checkpoint will be saved.
                 A possible value of this option is `alf.trainers.evaluator.BestEvalChecker()`,
@@ -383,6 +388,7 @@ def __init__(self,
         self.num_eval_episodes = num_eval_episodes
         self.num_eval_environments = num_eval_environments
         self.async_eval = async_eval
+        self.shared_train_eval_env = shared_train_eval_env
         self.save_checkpoint_for_best_eval = save_checkpoint_for_best_eval
         self.ddp_paras_check_interval = ddp_paras_check_interval
         self.num_summaries = num_summaries
diff --git a/alf/trainers/evaluator.py b/alf/trainers/evaluator.py
index dd6367900..897b7f7e1 100644
--- a/alf/trainers/evaluator.py
+++ b/alf/trainers/evaluator.py
@@ -74,10 +74,15 @@ def __init__(self, config: TrainerConfig, conf_file: str):
                       pre_configs, num_envs, config.root_dir, seed))
             self._worker.start()
         else:
-            self._env = create_environment(
-                for_evaluation=True,
-                num_parallel_environments=num_envs,
-                seed=seed)
+            if config.shared_train_eval_env:
+                assert not self._async, "should not use async_eval in shared_train_eval_env mode"
+                self._env = alf.get_env()
+                self._env.reset()
+            else:
+                self._env = create_environment(
+                    for_evaluation=True,
+                    num_parallel_environments=num_envs,
+                    seed=seed)
             self._evaluator = SyncEvaluator(self._env, config)
 
     def eval(self, algorithm: RLAlgorithm, step_metric_values: Dict[str, int]):