diff --git a/conda_subprocess/process.py b/conda_subprocess/process.py
index 5981588..960eb3f 100644
--- a/conda_subprocess/process.py
+++ b/conda_subprocess/process.py
@@ -18,6 +18,7 @@ def Popen(
     preexec_fn=None,
     close_fds=True,
     cwd=None,
+    env=None,
     prefix_name=None,
     prefix_path=None,
     universal_newlines=None,
@@ -52,6 +53,11 @@ def Popen(
     if not isiterable(command):
         command = shlex_split_unicode(command)
 
+    # update environment
+    environment_dict = os.environ.copy()
+    if env is not None:
+        environment_dict.update(env)
+
     # spawn subprocess
     return subprocess_Popen(
         args=encode_arguments(command),
@@ -63,7 +69,7 @@ def Popen(
         close_fds=close_fds,
         shell=False,
         cwd=cwd,
-        env=encode_environment(os.environ.copy()),
+        env=encode_environment(environment_dict),
         universal_newlines=universal_newlines,
         startupinfo=startupinfo,
         creationflags=creationflags,
diff --git a/tests/test_conda_subprocess.py b/tests/test_conda_subprocess.py
index f7634ab..d3d9c1a 100644
--- a/tests/test_conda_subprocess.py
+++ b/tests/test_conda_subprocess.py
@@ -49,3 +49,14 @@ def test_popen(self):
         else:
             self.assertEqual(output[0], b"Python 3.12.1\n")
         self.assertIsNone(output[1])
+
+    def test_environment_variable(self):
+        self.assertTrue(
+            "TESTVAR=test"
+            in check_output(
+                "env",
+                prefix_path=self.env_path,
+                env={"TESTVAR": "test"},
+                universal_newlines=True,
+            ).split("\n"),
+        )