The paper presents Ontology UML Profile (OUP); which, together with Ontology Definition Metamodel (ODM), enables the usage of Model Driven Architecture (MDA) standards in ontological engineering. Other similar metamodels and UML profiles are based on ontology representation languages, such as RDF(S), DAML+OIL, etc. However, none of these other solutions uses the recent W3C effort – The Web Ontology Language (OWL). In our approach, we firstly define the place of ODM and OUP in the context of the MDA four-layer architecture and identify the main OWL concepts. Then, to support ODM, we define OUP and describe its details. The proposed UML profile enables usage of the well-known UML notation in ontological engineering more extensively. We implemented an XSLT that transforms OUP ontologies into OWL in order to provide a suitable tool support.