The purpose of this study was to investigate the differences between two kinds of softball pitching techniques that involve pitching the arm backward. Two high skilled female fastpitch softball pitchers served as subjects. Two high-speed video cameras (120 frames/s) were synchronized to collect the arm motions during softball pitching. Angular momentum of the pitching arm was then calculated from these kinematic data and from the moment of inertia of the arm. The results indicated that the first-peak velocity (elbow: straight-arm backward style 5.95m/s＞curve-arm backward style 5.19m/s; wrist: straight-arm backward style 9.38m/s＞ curve-arm backward style 5.88m/s), moment of inertia(left leg landing: straight-arm backward style 0.34kg*m2＞curve-arm backward style 0.17kp*m2), and angular momentum (left leg landing: straight-arm backward style 3.92kg*m2/s＞curve-arm backward style 0.17kg*m22.11kg*m2/s)were larger for the straight-arm backward style during the preparation stage and of the transmission stage. It is suggested that the pitchers need to have better muscle endurance for the straight-arm backward style. However, the pitchers must have more muscle power and coordination for the curve-arm backward style.