The present paper considers the conceptual design of floating wave-offshore wind hybrid power generation system. The worldwide demand for ocean renewable energy is increasing rapidly. Wave and offshore wind energy have been more attractive than the others among the various ocean renewable energy sources, as the site to generate electricity from wave and offshore wind accord well together. It indicates that a hybrid power generation system, which uses wave energy and offshore wind energy simultaneously has many advantages. In order to take the advantage, technical developments for very large floating structure and system integration including wave and offshore wind power generation system are required. As a result, a R&D project for development of a 10MW class floating wave-offshore wind hybrid power generation system has been launched in Korea. In the project, a multiple wind turbines and wave energy converters were placed on a large moored floater based on parametric studies considering the interaction between the wind turbines and wave energy converters. A ring-typed semi-submersible platform, which has four vertical columns at each corner of the platform to be connected with horizontal pontoons, was introduced for this system. A proper wave energy converter and power converting systems were also developed. In the present paper, those results will be presented and the difficulties in the design of hybrid power generation system are discussed.