The vision of ontology research has recently drawn considerable attention, both from academia and industry. One of the essential research issues with ontology is how to describe changes during its evolving cycle, especially in virtual enterprises which exist as a temporary network o€ geographically distributed partners that assemble to achieve a goal. Ontology refinement is a crucial component in ontology evolution. Description logics are very useful for defining and maintaining ontologies, including ontology consistency checking. In this paper, a taxonomy is adopted to describe ontologies with an intuitive ontology definition formula. Based on the ontology definition, a novel agent-based approach is presented which deals with ontology refinement at run-time in virtual enterprises. We demonstrate the method with a running example by using the JADE platform.