Linear theories were developed for the analysis of the wave induced oscillation of a linearly moored floating body of rectangular cross section by Ijima and Ito. These linear theories ignore viscous resistance and assume the mooring system to be linear. On the other hand, in practical situation, viscous resistance plays an important role for resonant phenomenon, and the mooring system need not have linear characteristics.
　The purpose of this study is to examine the validity of applying perio-resistance for linearly moored floating body, and to examine the effect of the characteristics of the mooring system, such as linear or non-linear, or symmetry or asymmetry, on the motion and mooring force of the floating body.
　The analysis yields the following conclusion.
　The viscous resistance arises form the generation of eddies at both corners of the bilge. Provided by an adequate coefficient for the viscous resistance, the equation of motion gives relevant solution of the motion. Even undernon-linear and asymmetric mooring condition as well as linear one, the equation of motion yields pertinent estimates of mooring forces.