diff --git a/google/auth/aws.py b/google/auth/aws.py
index b362dd3..c2b521c 100644
--- a/google/auth/aws.py
+++ b/google/auth/aws.py
@@ -424,9 +424,9 @@
 
         The logic is summarized as:
 
-        Retrieve the AWS region from the AWS_REGION environment variable or from
-        the AWS metadata server availability-zone if not found in the
-        environment variable.
+        Retrieve the AWS region from the AWS_REGION or AWS_DEFAULT_REGION
+        environment variable or from the AWS metadata server availability-zone
+        if not found in the environment variable.
 
         Check AWS credentials in environment variables. If not found, retrieve
         from the AWS metadata server security-credentials endpoint.
@@ -504,8 +504,8 @@
         )
 
     def _get_region(self, request, url):
-        """Retrieves the current AWS region from either the AWS_REGION
-        environment variable or from the AWS metadata server.
+        """Retrieves the current AWS region from either the AWS_REGION or
+        AWS_DEFAULT_REGION environment variable or from the AWS metadata server.
 
         Args:
             request (google.auth.transport.Request): A callable used to make
@@ -526,6 +526,10 @@
         if env_aws_region is not None:
             return env_aws_region
 
+        env_aws_region = os.environ.get(environment_vars.AWS_DEFAULT_REGION)
+        if env_aws_region is not None:
+            return env_aws_region
+
         if not self._region_url:
             raise exceptions.RefreshError("Unable to determine AWS region")
         response = request(url=self._region_url, method="GET")
diff --git a/google/auth/environment_vars.py b/google/auth/environment_vars.py
index 416bab0..f027741 100644
--- a/google/auth/environment_vars.py
+++ b/google/auth/environment_vars.py
@@ -69,3 +69,4 @@
 AWS_SECRET_ACCESS_KEY = "AWS_SECRET_ACCESS_KEY"
 AWS_SESSION_TOKEN = "AWS_SESSION_TOKEN"
 AWS_REGION = "AWS_REGION"
+AWS_DEFAULT_REGION = "AWS_DEFAULT_REGION"