This paper presents an ontology-based approach to resolve conflicts in collaborative design. In a collaborative design environment, achieving a global design of a product implies the proposed model is realisable and acceptable to all participants involved in the design project. Whenever this does not happen we have a conflicting situation. The work presented here is based on the use of ontology modelling (OWL) to represent knowledge and, like that, to enable a reasoning process to be done. The results of this reasoning, the conflicting axioms detected, are used as starting point to a conflict resolution process. First, an automatic approach is tried. In case of failure, the next step is the direct interaction among the project participants, i.e., negotiation and mediation. A small electrical connector was taken as example to illustrate our approach.