diff --git a/openapi_core/schema/schemas/factories.py b/openapi_core/schema/schemas/factories.py
index d0fb7cc..b054898 100644
--- a/openapi_core/schema/schemas/factories.py
+++ b/openapi_core/schema/schemas/factories.py
@@ -28,6 +28,7 @@ class SchemaFactory(object):
         deprecated = schema_deref.get('deprecated', False)
         all_of_spec = schema_deref.get('allOf', None)
         one_of_spec = schema_deref.get('oneOf', None)
+        additional_properties_spec = schema_deref.get('additionalProperties')
 
         properties = None
         if properties_spec:
@@ -45,11 +46,16 @@ class SchemaFactory(object):
         if items_spec:
             items = self._create_items(items_spec)
 
+        additional_properties = None
+        if additional_properties_spec:
+            additional_properties = self.create(additional_properties_spec)
+
         return Schema(
             schema_type=schema_type, model=model, properties=properties,
             items=items, schema_format=schema_format, required=required,
             default=default, nullable=nullable, enum=enum,
             deprecated=deprecated, all_of=all_of, one_of=one_of,
+            additional_properties=additional_properties,
         )
 
     @property
diff --git a/openapi_core/schema/schemas/models.py b/openapi_core/schema/schemas/models.py
index 624839c..4e37cde 100644
--- a/openapi_core/schema/schemas/models.py
+++ b/openapi_core/schema/schemas/models.py
@@ -28,7 +28,8 @@ class Schema(object):
     def __init__(
             self, schema_type=None, model=None, properties=None, items=None,
             schema_format=None, required=None, default=None, nullable=False,
-            enum=None, deprecated=False, all_of=None, one_of=None):
+            enum=None, deprecated=False, all_of=None, one_of=None,
+            additional_properties=None):
         self.type = schema_type and SchemaType(schema_type)
         self.model = model
         self.properties = properties and dict(properties) or {}
@@ -41,6 +42,7 @@ class Schema(object):
         self.deprecated = deprecated
         self.all_of = all_of and list(all_of) or []
         self.one_of = one_of and list(one_of) or []
+        self.additional_properties = additional_properties
 
         self._all_required_properties_cache = None
         self._all_optional_properties_cache = None
@@ -183,11 +185,16 @@ class Schema(object):
 
         value_props_names = value.keys()
         extra_props = set(value_props_names) - set(all_props_names)
-        if extra_props:
+        if extra_props and self.additional_properties is None:
             raise UndefinedSchemaProperty(
                 "Undefined properties in schema: {0}".format(extra_props))
 
         properties = {}
+        for prop_name in extra_props:
+            prop_value = value[prop_name]
+            properties[prop_name] = self.additional_properties.unmarshal(
+                prop_value)
+
         for prop_name, prop in iteritems(all_props):
             try:
                 prop_value = value[prop_name]
diff --git a/tests/integration/data/v3.0/petstore.yaml b/tests/integration/data/v3.0/petstore.yaml
index d788ebb..0e837e4 100644
--- a/tests/integration/data/v3.0/petstore.yaml
+++ b/tests/integration/data/v3.0/petstore.yaml
@@ -284,6 +284,8 @@ components:
           properties:
             rootCause:
               type: string
+      additionalProperties:
+        type: string
   responses:
       ErrorResponse:
         description: unexpected error
diff --git a/tests/integration/test_petstore.py b/tests/integration/test_petstore.py
index b3ed51d..9b41617 100644
--- a/tests/integration/test_petstore.py
+++ b/tests/integration/test_petstore.py
@@ -757,3 +757,38 @@ class TestPetstore(object):
 
         with pytest.raises(InvalidMediaTypeValue):
             request.get_body(spec)
+
+    def test_post_tags_additional_properties(
+            self, spec, response_validator):
+        host_url = 'http://petstore.swagger.io/v1'
+        path_pattern = '/v1/tags'
+        pet_name = 'Dog'
+        data_json = {
+            'name': pet_name,
+        }
+        data = json.dumps(data_json)
+
+        request = MockRequest(
+            host_url, 'POST', '/tags',
+            path_pattern=path_pattern, data=data,
+        )
+
+        parameters = request.get_parameters(spec)
+        body = request.get_body(spec)
+
+        assert parameters == {}
+        assert body == data_json
+
+        data_json = {
+            'code': 400,
+            'message': 'Bad request',
+            'rootCause': 'Tag already exist',
+            'additionalinfo': 'Tag Dog already exist',
+        }
+        data = json.dumps(data_json)
+        response = MockResponse(data, status_code=404)
+
+        response_result = response_validator.validate(request, response)
+
+        assert response_result.errors == []
+        assert response_result.data == data_json