Domain knowledge may be used in medical applications to avoid wrong decisions and also to be able to make a correct decision for strong working diagnosis and partly for therapeutic purpose. In this paper, Case Based Reasoning (CBR) methodology has been applied by combining with ontology for implementing case-based medical diagnostic knowledge structure. The development of knowledge repository for disease-specific treatment has proposed in order to support diagnosis process, provide and share the knowledge of medical experts for diagnostic process and treatment of specific disease. It has also been described that medical Knowledge Base (KB) systems are either highly specialize, lack accuracy or are just too simple. To overcome this problem of scope, this paper describes a methodology for proliferating the scope and precision of the diagnostic ontology-based knowledge base. It also aims to understand and solve new similar problems and support similar decision making as well as share medical knowledge and treatment experiences among the medical practitioners. The application area is concerning a common and often deadly infectious disease, tuberculosis (TB) especially the pulmonary TB.