Proper names often constitute a problem in translation. This contribution deals with an ontology which represents the basis for a multilingual database of proper names, Prolexbase. It is being set up for treatment of proper names in the framework of the Prolex project. The aim of this contribution is to create a multilingual database of proper names containing information applicable to machine translation, computer aided translation, data research as well as spelling dictionaries. These particular aims guided the creation of the ontology whose description will follow. Beside a set of language-dependent and language-independent relations associated with a logical model, the database is founded on a four level ontology: the level of instances, the linguistic level, the conceptual level and the metaconceptual level. The authors describe here the different levels of the ontology and their implementation in the database using French and German examples.