This paper deals with a new concept by combining a monopile type wind turbine and a heave-type wave energy converter, that is referred as the ‘MWWC’ (Monopile-WT-WEC- Combination) system herein. Hydrodynamic responses of the MWWC system under typical operational seas cases have been investigated by using both time-domain numerical simulations and scale model tests (1:50). For the numerical model, hydrodynamic loads of the monopile and the WEC are calculated by the AQWA code, which is available for modeling multi-body systems including both mechanical and hydrodynamic couplings between the TLP and the WEC. The scale model tests have been done in State Key Laboratory of Costal and Offshore Engineering (SLCOE). The power-take-off (PTO) system of the WEC device is simulated by two nonlinear air-dampers. Main hydrodynamic characteristics of the MWWC system under typical operational sea cases have been clarified. The obtained wave power characteristic and maximum PTO damping force of the WEC are very helpful for the optimal design of the operational performance of the PTO system. Numerical and experimental results are presented and compared, and good agreements are achieved.