A double-submerged breakwater, which is a pair of small submerged breakwaters placed some distance apart, is considered to obtain more desirable wave field than a conventional single-submerged breakwater. Wave tank experiments using random waves of several significant waves were conducted for double- and single-submerged breakwaters. Spatial changes of wave amplitude spectra and flow velocity spectra, mean water level change, skewness and atiltness of the wave profile of the water surface and the bottom velocity oscillations were calculated. The single-submerged breakwater generally shows better wave interception, while the double-submerged breakwater has less mean water level change, less steady flow velocity and less asymmetry wave profile of the flow velocity at the bottom. It is also found that very low frequency oscillation arises in surface waves and flow velocity at the bottom, especially for the single-submerged breakwaters.