As the complexity of engineering design environment has been increased, it becomes difficult to exchange design data among design support systems. The purpose of this paper is to develop the XML-based Generalized Mechanical Data Exchange Formats(GMDEF) independent of specific mechanical element and to improve the interoperability of them using ontology, in order to integrate diverse design data and facilitate communication between design support systems. GMDEF consists of PartDoc and AssemblyDoc. PartDoc represents the information of a single part. AssemblyDoc represents the relation of parts composing an assembly. GMDEF is validated by GMDEF Schema. GMDEF Schema consists of separated XML Schemas and has flexible architecture to facilitate extension. The ontology is applied to GMDEF Schema to share and reuse vocabularies of specific mechanical elements.