diff --git a/moto/rds/models.py b/moto/rds/models.py
index f4ad42687..37c7f3f30 100644
--- a/moto/rds/models.py
+++ b/moto/rds/models.py
@@ -1385,6 +1385,15 @@ class RDSBackend(BaseBackend):
 
         return self.database_snapshots.pop(db_snapshot_identifier)
 
+    def promote_read_replica(self, db_kwargs):
+        database_id = db_kwargs["db_instance_identifier"]
+        database = self.databases.get(database_id)
+        if database.is_replica:
+            database.is_replica = False
+            database.update(db_kwargs)
+
+        return database
+
     def create_db_instance_read_replica(self, db_kwargs):
         database_id = db_kwargs["db_instance_identifier"]
         source_database_id = db_kwargs["source_db_identifier"]
diff --git a/moto/rds/responses.py b/moto/rds/responses.py
index b16ab47e7..814e9d828 100644
--- a/moto/rds/responses.py
+++ b/moto/rds/responses.py
@@ -295,6 +295,14 @@ class RDSResponse(BaseResponse):
         template = self.response_template(DESCRIBE_SNAPSHOTS_TEMPLATE)
         return template.render(snapshots=snapshots)
 
+    def promote_read_replica(self):
+        db_instance_identifier = self._get_param("DBInstanceIdentifier")
+        db_kwargs = self._get_db_kwargs()
+        database = self.backend.promote_read_replica(db_kwargs)
+        database = self.backend.modify_db_instance(db_instance_identifier, db_kwargs)
+        template = self.response_template(PROMOTE_REPLICA_TEMPLATE)
+        return template.render(database=database)
+
     def delete_db_snapshot(self):
         db_snapshot_identifier = self._get_param("DBSnapshotIdentifier")
         snapshot = self.backend.delete_db_snapshot(db_snapshot_identifier)
@@ -704,6 +712,15 @@ MODIFY_DATABASE_TEMPLATE = """<ModifyDBInstanceResponse xmlns="http://rds.amazon
   </ResponseMetadata>
 </ModifyDBInstanceResponse>"""
 
+PROMOTE_REPLICA_TEMPLATE = """<PromoteReadReplicaResponse xmlns="http://rds.amazonaws.com/doc/2014-09-01/">
+  <PromoteReadReplicaResult>
+  {{ database.to_xml() }}
+  </PromoteReadReplicaResult>
+  <ResponseMetadata>
+    <RequestId>8e8c0d64-be21-11d3-a71c-13dc2f771e41</RequestId>
+  </ResponseMetadata>
+</PromoteReadReplicaResponse>"""
+
 REBOOT_DATABASE_TEMPLATE = """<RebootDBInstanceResponse xmlns="http://rds.amazonaws.com/doc/2014-09-01/">
   <RebootDBInstanceResult>
   {{ database.to_xml() }}
diff --git a/tests/test_rds/test_rds.py b/tests/test_rds/test_rds.py
index 67567772b..006903788 100644
--- a/tests/test_rds/test_rds.py
+++ b/tests/test_rds/test_rds.py
@@ -656,6 +656,34 @@ def test_describe_db_snapshots():
     snapshots.should.have.length_of(2)
 
 
+@mock_rds
+def test_promote_read_replica():
+    conn = boto3.client("rds", region_name="us-west-2")
+    conn.create_db_instance(
+        DBInstanceIdentifier="db-primary-1",
+        AllocatedStorage=10,
+        Engine="postgres",
+        DBName="staging-postgres",
+        DBInstanceClass="db.m1.small",
+        MasterUsername="root",
+        MasterUserPassword="hunter2",
+        Port=1234,
+        DBSecurityGroups=["my_sg"],
+    )
+
+    conn.create_db_instance_read_replica(
+        DBInstanceIdentifier="db-replica-1",
+        SourceDBInstanceIdentifier="db-primary-1",
+        DBInstanceClass="db.m1.small",
+    )
+    conn.promote_read_replica(DBInstanceIdentifier="db-replica-1")
+
+    replicas = conn.describe_db_instances(DBInstanceIdentifier="db-primary-1").get(
+        "ReadReplicaDBInstanceIdentifiers"
+    )
+    assert replicas is None
+
+
 @mock_rds
 def test_delete_db_snapshot():
     conn = boto3.client("rds", region_name="us-west-2")