diff --git a/google/cloud/bigquery/model.py b/google/cloud/bigquery/model.py
index 1143b71f9..6fdfc5596 100644
--- a/google/cloud/bigquery/model.py
+++ b/google/cloud/bigquery/model.py
@@ -18,7 +18,7 @@
 
 import copy
 
-from google.protobuf import json_format
+import json
 import six
 
 import google.cloud._helpers
@@ -55,7 +55,7 @@ class Model(object):
     def __init__(self, model_ref):
         # Use _proto on read-only properties to use it's built-in type
         # conversion.
-        self._proto = types.Model()._pb
+        self._proto = types.Model()
 
         # Use _properties on read-write properties to match the REST API
         # semantics. The BigQuery API makes a distinction between an unset
@@ -67,7 +67,7 @@ def __init__(self, model_ref):
             model_ref = ModelReference.from_string(model_ref)
 
         if model_ref:
-            self._proto.model_reference.CopyFrom(model_ref._proto)
+            self._proto.model_reference = model_ref._proto
 
     @property
     def reference(self):
@@ -305,9 +305,7 @@ def from_api_repr(cls, resource):
             start_time = datetime_helpers.from_microseconds(1e3 * float(start_time))
             training_run["startTime"] = datetime_helpers.to_rfc3339(start_time)
 
-        this._proto = json_format.ParseDict(
-            resource, types.Model()._pb, ignore_unknown_fields=True
-        )
+        this._proto = types.Model.from_json(json.dumps(resource))
         return this
 
     def _build_resource(self, filter_fields):
@@ -323,7 +321,7 @@ def to_api_repr(self):
         Returns:
             Dict[str, object]: Model reference represented as an API resource
         """
-        return json_format.MessageToDict(self._proto)
+        return json.loads(types.Model.to_json(self._proto))
 
 
 class ModelReference(object):
@@ -334,7 +332,7 @@ class ModelReference(object):
     """
 
     def __init__(self):
-        self._proto = types.ModelReference()._pb
+        self._proto = types.ModelReference()
         self._properties = {}
 
     @property
@@ -377,9 +375,7 @@ def from_api_repr(cls, resource):
         # Keep a reference to the resource as a workaround to find unknown
         # field values.
         ref._properties = resource
-        ref._proto = json_format.ParseDict(
-            resource, types.ModelReference()._pb, ignore_unknown_fields=True
-        )
+        ref._proto = types.ModelReference.from_json(json.dumps(resource))
 
         return ref
 
@@ -418,7 +414,7 @@ def to_api_repr(self):
         Returns:
             Dict[str, object]: Model reference represented as an API resource
         """
-        return json_format.MessageToDict(self._proto)
+        return json.loads(types.ModelReference.to_json(self._proto))
 
     def _key(self):
         """Unique key for this model.
diff --git a/tests/unit/model/test_model.py b/tests/unit/model/test_model.py
index 9fa29a496..1d7605d54 100644
--- a/tests/unit/model/test_model.py
+++ b/tests/unit/model/test_model.py
@@ -123,21 +123,21 @@ def test_from_api_repr(target_class):
     assert got.training_runs[0].training_options.initial_learn_rate == 1.0
     assert (
         got.training_runs[0]
-        .start_time.ToDatetime()
+        .start_time
         .replace(tzinfo=google.cloud._helpers.UTC)
         == creation_time
     )
     assert got.training_runs[1].training_options.initial_learn_rate == 0.5
     assert (
         got.training_runs[1]
-        .start_time.ToDatetime()
+        .start_time
         .replace(tzinfo=google.cloud._helpers.UTC)
         == modified_time
     )
     assert got.training_runs[2].training_options.initial_learn_rate == 0.25
     assert (
         got.training_runs[2]
-        .start_time.ToDatetime()
+        .start_time
         .replace(tzinfo=google.cloud._helpers.UTC)
         == expiration_time
     )
@@ -321,7 +321,7 @@ def test_repr(target_class):
 
 
 def test_to_api_repr(target_class):
-    from google.protobuf import json_format
+    import json
 
     model = target_class("my-proj.my_dset.my_model")
     resource = {
@@ -357,8 +357,6 @@ def test_to_api_repr(target_class):
             "kmsKeyName": "projects/1/locations/us/keyRings/1/cryptoKeys/1"
         },
     }
-    model._proto = json_format.ParseDict(
-        resource, types.Model()._pb, ignore_unknown_fields=True
-    )
+    model._proto = types.Model.from_json(json.dumps(resource))
     got = model.to_api_repr()
     assert got == resource