Abstract The purpose of this thesis is to create the ontology of the domain knowledge of “Mechatronic Engineering”, based on the existed semantic web environment, including automatic mechanism design, mechanical movement functions (movement modes, cycles, speed and power sources etc.), materials, manufacturing and the control circuits. The knowledge of Mechatronic Engineering is diverse and can be analyzed from many perspectives such as design, mechanism functions, material characteristics and manufacturing processes. Besides, domain knowledge is usually implicit instead of explicit. Therefore, it requires extra notes from an expert before the implicit knowledge can be translated into explicit knowledge which become popularization. A function has to be defined first during automatic design phase. In order to accomplish this function, it is necessary to come up with a significant amount of mechanism components, combine connecting rod combinations and power sources as well as the system’s circuit design. Then, it is required to evaluate the benefits and shortcomings of the design methods before the designed mechanism can be employed. The knowledge of Mechatronic Engineering is huge and complicate. It must be equipped with a powerful knowledge base to serve the needs of reference and upgrowth. However, the accomplishment of this study will enable the experts to record annotations to the knowledge of Mechatronic Engineering so that the knowledge may be stored, updated and reused. Keyword:Ontology, Automatic Mechanism, Knowledge System ,Semantic Web.