In this paper, the motion responses with hydrodynamic interaction effect between two off-shore floating structures in various heading waves are studied by using a linearized three-dimensional potential theory. Numerical calculations using three-dimensional pulsating source distribution techniques have been carried out for twelve coupled linear motion responses and relative motions of the barge and the ship in oblique waves. The computational results give a good correlation with the experimental results and also with other numerical results. As a result, the present computational tool can be used effectively to predict the motion responses of multiple offshore floating structures in waves.