Mastitis is a cow disease caused by an infection in the mammary gland due to bacteria entering through the skin. This disease can have repercussions directly on the quality of the milk and thus, on the incomes of the producers. Therefore, the objective of this work was creating ontology with mastitis in order to provide a tool for veterinarians, which helps in the search of information related to different cases and treatments. Methontology and Protégé methodologies were respectively used in order to develop and formalize the ontology. As a result of the process, it was obtained an ontology integration model for mastitis, with an information system for medical diagnose.