An experimental and numerical investigation was made to examine the characteristics of pontoon type floating breakwaters(FBW) in regular waves. Motion responses of FBW and wave transmission coefficients are observed and compared with the results based on the linear potential theory. The linear potential theory is found to be a successful tool to investigate the characteristics of the floating breakwaters. We confirm that there exists a minimum wave transmission coefficient which is a function of wave-length/beam and beam/draft ratio. As beam/draft ratio increases the value of wave-length/beam ratio where the minimum, wave transmission coefficient occurs increases. Excessive mooring stiffness can deteriorate the performance of the floating breakwaters.