Aerodynamic performance of a Japanese traditional square rig, “Bezai-ho”, and a Chinese lug rig, “Shinshi-bo” in Japanese, were studied by means of wind tunnel tests, sea trials and numerical calculations. Sail forces and sail shapes were measured in the wind tunnel tests. A sail dynamometer boat Fujin was employed for the sea trials, by which aerodynamic forces acting on sail, sail shapes, and sailing conditions of the boat can be measured at the same time. Using the measured sail shapes, sail forces are calculated by means of a vortex lattice method. Differences of sail performance of the above mentioned two types of rig were clarified in the wind tunnel tests and sea trials. The calculated sail performance shows good agreements with the measured data in upwind condition.