diff --git a/ceilometer/compute/virt/xenapi/inspector.py b/ceilometer/compute/virt/xenapi/inspector.py
index 62960da3d9..9632cbaec9 100644
--- a/ceilometer/compute/virt/xenapi/inspector.py
+++ b/ceilometer/compute/virt/xenapi/inspector.py
@@ -135,12 +135,23 @@ class XenapiInspector(virt_inspector.Inspector):
     def inspect_memory_usage(self, instance, duration=None):
         instance_name = util.instance_name(instance)
         vm_ref = self._lookup_by_name(instance_name)
-        metrics_ref = self._call_xenapi("VM.get_metrics", vm_ref)
-        metrics_rec = self._call_xenapi("VM_metrics.get_record",
-                                        metrics_ref)
-        # Stat provided from XenServer is in B, converting it to MB.
-        memory = int(metrics_rec['memory_actual']) / units.Mi
-        return virt_inspector.MemoryUsageStats(usage=memory)
+        total_mem = float(self._call_xenapi("VM.query_data_source",
+                                            vm_ref,
+                                            "memory"))
+        try:
+            free_mem = float(self._call_xenapi("VM.query_data_source",
+                                               vm_ref,
+                                               "memory_internal_free"))
+        except api.Failure:
+            # If PV tools is not installed in the guest instance, it's
+            # impossible to get free memory. So give it a default value
+            # as 0.
+            free_mem = 0
+        # memory provided from XenServer is in Bytes;
+        # memory_internal_free provided from XenServer is in KB,
+        # converting it to MB.
+        memory_usage = (total_mem - free_mem * units.Ki) / units.Mi
+        return virt_inspector.MemoryUsageStats(usage=memory_usage)
 
     def inspect_vnic_rates(self, instance, duration=None):
         instance_name = util.instance_name(instance)
diff --git a/ceilometer/tests/unit/compute/virt/xenapi/fake_XenAPI.py b/ceilometer/tests/unit/compute/virt/xenapi/fake_XenAPI.py
new file mode 100644
index 0000000000..1f33f78489
--- /dev/null
+++ b/ceilometer/tests/unit/compute/virt/xenapi/fake_XenAPI.py
@@ -0,0 +1,19 @@
+# Copyright 2016 Citrix
+#
+# Licensed under the Apache License, Version 2.0 (the "License"); you may
+# not use this file except in compliance with the License. You may obtain
+# a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+# WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+# License for the specific language governing permissions and limitations
+# under the License.
+"""fake XenAPI for testing in case XenAPI doesn't exist in the test env"""
+
+
+class Failure(Exception):
+    def __init__(self, details):
+        self.details = details
diff --git a/ceilometer/tests/unit/compute/virt/xenapi/test_inspector.py b/ceilometer/tests/unit/compute/virt/xenapi/test_inspector.py
index d84853babc..caa1c93793 100644
--- a/ceilometer/tests/unit/compute/virt/xenapi/test_inspector.py
+++ b/ceilometer/tests/unit/compute/virt/xenapi/test_inspector.py
@@ -19,6 +19,7 @@ from oslotest import base
 
 from ceilometer.compute.virt import inspector as virt_inspector
 from ceilometer.compute.virt.xenapi import inspector as xenapi_inspector
+from ceilometer.tests.unit.compute.virt.xenapi import fake_XenAPI
 
 
 class TestSwapXapiHost(base.BaseTestCase):
@@ -81,25 +82,59 @@ class TestXenapiInspection(base.BaseTestCase):
     def test_inspect_memory_usage(self):
         fake_instance = {'OS-EXT-SRV-ATTR:instance_name': 'fake_instance_name',
                          'id': 'fake_instance_id'}
-        fake_stat = virt_inspector.MemoryUsageStats(usage=128)
+        fake_stat = virt_inspector.MemoryUsageStats(usage=64)
 
-        def fake_xenapi_request(method, args):
-            metrics_rec = {
-                'memory_actual': '134217728',
-            }
+        def _fake_xenapi_request(method, args):
+            fake_total_mem = 134217728.0
+            fake_free_mem = 65536.0
 
             if method == 'VM.get_by_name_label':
                 return ['vm_ref']
-            elif method == 'VM.get_metrics':
-                return 'metrics_ref'
-            elif method == 'VM_metrics.get_record':
-                return metrics_rec
+            elif method == 'VM.query_data_source':
+                if 'memory' in args:
+                    return fake_total_mem
+                elif 'memory_internal_free' in args:
+                    return fake_free_mem
+                else:
+                    return None
             else:
                 return None
 
         session = self.inspector.session
         with mock.patch.object(session, 'xenapi_request',
-                               side_effect=fake_xenapi_request):
+                               side_effect=_fake_xenapi_request):
+            memory_stat = self.inspector.inspect_memory_usage(fake_instance)
+            self.assertEqual(fake_stat, memory_stat)
+
+    def test_inspect_memory_usage_without_freeMem(self):
+        fake_instance = {'OS-EXT-SRV-ATTR:instance_name': 'fake_instance_name',
+                         'id': 'fake_instance_id'}
+        fake_stat = virt_inspector.MemoryUsageStats(usage=128)
+
+        def _fake_xenapi_request(method, args):
+            if xenapi_inspector.api is None:
+                # the XenAPI may not exist in the test environment.
+                # In that case, we use the fake XenAPI for testing.
+                xenapi_inspector.api = fake_XenAPI
+            fake_total_mem = 134217728.0
+            fake_details = ['INTERNAL_ERROR',
+                            'Rrd.Invalid_data_source("memory_internal_free")']
+
+            if method == 'VM.get_by_name_label':
+                return ['vm_ref']
+            elif method == 'VM.query_data_source':
+                if 'memory' in args:
+                    return fake_total_mem
+                elif 'memory_internal_free' in args:
+                    raise xenapi_inspector.api.Failure(fake_details)
+                else:
+                    return None
+            else:
+                return None
+
+        session = self.inspector.session
+        with mock.patch.object(session, 'xenapi_request',
+                               side_effect=_fake_xenapi_request):
             memory_stat = self.inspector.inspect_memory_usage(fake_instance)
             self.assertEqual(fake_stat, memory_stat)