The development of a cost-effective wind turbine system of floating-type is of interest in the renewable energy industry. A study on the SPAR-type floating foundations using reinforced concrete was carried out. Regular and irregular wave experiments were performed for 1/100 scale models of the prototypes. Three models were examined, i.e., a uniform cylinder moored at the gravity center, a uniform cylinder moored at the upper position, and a stepped-type floating cylinder moored at the upper position. Higher attachment of the mooring lines gave smaller response in pitch. The stepped-type SPAR had smaller response characteristics in heave and pitch than the simple SPAR. This is an abstract of a paper presented at the 2009 International Offshore and Polar Engineering Conference (Osaka, Japan 6/21-26/2009).