diff --git a/neutron/db/migration/alembic_migrations/versions/EXPAND_HEAD b/neutron/db/migration/alembic_migrations/versions/EXPAND_HEAD
index ae416390415..3bd1cc3f361 100644
--- a/neutron/db/migration/alembic_migrations/versions/EXPAND_HEAD
+++ b/neutron/db/migration/alembic_migrations/versions/EXPAND_HEAD
@@ -1 +1 @@
-659cbedf30a1
+21ff98fabab1
diff --git a/neutron/db/migration/alembic_migrations/versions/zed/expand/21ff98fabab1_add_ndp_proxy_constraint.py b/neutron/db/migration/alembic_migrations/versions/zed/expand/21ff98fabab1_add_ndp_proxy_constraint.py
new file mode 100644
index 00000000000..b4e5be72bc4
--- /dev/null
+++ b/neutron/db/migration/alembic_migrations/versions/zed/expand/21ff98fabab1_add_ndp_proxy_constraint.py
@@ -0,0 +1,37 @@
+# Copyright 2022 OpenStack Foundation
+#
+#    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.
+#
+
+from alembic import op
+
+
+"""add ndp proxy constraint
+
+Revision ID: 21ff98fabab1
+Revises: 659cbedf30a1
+Create Date: 2022-05-22 14:16:24.550155
+
+"""
+
+# revision identifiers, used by Alembic.
+revision = '21ff98fabab1'
+down_revision = '659cbedf30a1'
+
+
+def upgrade():
+    op.create_unique_constraint(
+        'uniq_ndp_proxy0router_id0ip_address',
+        'ndp_proxies',
+        ['router_id', 'ip_address']
+    )
diff --git a/neutron/db/models/ndp_proxy.py b/neutron/db/models/ndp_proxy.py
index 2cdf025f71a..7653018a90c 100644
--- a/neutron/db/models/ndp_proxy.py
+++ b/neutron/db/models/ndp_proxy.py
@@ -28,6 +28,12 @@ class NDPProxy(standard_attr.HasStandardAttributes,
                model_base.HasProject):
 
     __tablename__ = 'ndp_proxies'
+    __table_args__ = (
+        sa.UniqueConstraint(
+            'router_id', 'ip_address',
+            name='uniq_ndp_proxy0router_id0ip_address'),
+        model_base.BASEV2.__table_args__
+    )
 
     name = sa.Column(sa.String(db_const.NAME_FIELD_SIZE))
     router_id = sa.Column(sa.String(db_const.UUID_FIELD_SIZE),
diff --git a/neutron/services/ndp_proxy/exceptions.py b/neutron/services/ndp_proxy/exceptions.py
index 15e5b7e8708..f967783b290 100644
--- a/neutron/services/ndp_proxy/exceptions.py
+++ b/neutron/services/ndp_proxy/exceptions.py
@@ -37,7 +37,7 @@ class AddressScopeConflict(n_exc.Conflict):
 
 
 class RouterGatewayNotValid(n_exc.Conflict):
-    message = _("Can not enable ndp proxy no "
+    message = _("Can not enable ndp proxy on "
                 "router %(router_id)s, %(reason)s.")
 
 
@@ -62,4 +62,4 @@ class RouterIPv6GatewayInUse(n_exc.Conflict):
 
 
 class NDPProxyNotFound(n_exc.NotFound):
-    message = _("NDP proxy %(id)s could not be found.")
+    message = _("Ndp proxy %(id)s could not be found.")
diff --git a/neutron/tests/unit/extensions/test_l3_ndp_proxy.py b/neutron/tests/unit/extensions/test_l3_ndp_proxy.py
index 6f83c602d33..7f8dd960c95 100644
--- a/neutron/tests/unit/extensions/test_l3_ndp_proxy.py
+++ b/neutron/tests/unit/extensions/test_l3_ndp_proxy.py
@@ -247,7 +247,7 @@ class L3NDPProxyTestCase(test_address_scope.AddressScopeTestCase,
     def test_enable_ndp_proxy_without_external_gateway(self):
         with self.router() as router:
             router_id = router['router']['id']
-            err_msg = ("Can not enable ndp proxy no router %s, The router has "
+            err_msg = ("Can not enable ndp proxy on router %s, The router has "
                        "no external gateway or the external gateway port has "
                        "no IPv6 address.") % router_id
             self._update_router(router_id, {'enable_ndp_proxy': True},
@@ -260,7 +260,7 @@ class L3NDPProxyTestCase(test_address_scope.AddressScopeTestCase,
             self._update_router(
                 router_id,
                 {'external_gateway_info': {'network_id': self.ext_net_id}})
-            err_msg = ("Can not enable ndp proxy no router %s, The router's "
+            err_msg = ("Can not enable ndp proxy on router %s, The router's "
                        "external gateway will be unset.") % router_id
             self._update_router(
                 router_id,
@@ -516,3 +516,10 @@ class L3NDPProxyTestCase(test_address_scope.AddressScopeTestCase,
             self.assertTrue(router_dict['router']['enable_ndp_proxy'])
             self._create_ndp_proxy(
                 router_id, port_id)
+
+    def test_create_ndp_proxy_with_duplicated(self):
+        with self.port(self.private_subnet) as port1:
+            self._create_ndp_proxy(self.router1_id, port1['port']['id'])
+            self._create_ndp_proxy(
+                self.router1_id, port1['port']['id'],
+                expected_code=exc.HTTPConflict.code)
diff --git a/releasenotes/notes/forbid-duplicate-ndp-proxy-entry-28040bc2afb3c1c7.yaml b/releasenotes/notes/forbid-duplicate-ndp-proxy-entry-28040bc2afb3c1c7.yaml
new file mode 100644
index 00000000000..a3ff5dde941
--- /dev/null
+++ b/releasenotes/notes/forbid-duplicate-ndp-proxy-entry-28040bc2afb3c1c7.yaml
@@ -0,0 +1,6 @@
+---
+fixes:
+  - |
+    Forbid the creation of a duplicate NDP proxy entry on the same router,
+    since the IP address of a router is unique and an IPv6 address only needs
+    one NDP proxy.