Contemporary researches have revealed that most of the diseases are genetic. It is very important to mine the relation between gene and disease. Ontology is the best method to show the concepts and their relations. This research paper focuses on the development of ontology for the domain of Genetic Diseases. The data is extracted from UMLS. We developed this ontology on Protégé tool to facilitate the end users and clinical researchers. The resultant ontology is evaluated by domain experts.