This paper presents a Model-Based graphical editor for supporting the creation of conceptual models and domain ontologies in a philosophically and cognitively well-founded modeling language named OntoUML. The Editor is designed in a way that, on one hand, it shields the user from the complexity of the ontological principles underlying this language. On the other hand, it reinforces these principles in the produced models by providing a mechanism for automatic formal constraint verification. Keywords. Ontology Engineering, Conceptual Modeling.