The difference between the dominant hand and the non-dominant hand in overarm throwing motions and ball-throwing distances were studied in student women. The subjects were divided into a trained group and an untrained group. A switch thrower, categorized in the training group, was also examined. The throwing time, moving distance and mean velocity of the ball in the overall throwing phase, back-swing phase and acceleration phase were determined by a high-speed video analysis system. Seven empirical parameters estimated from the overall throwing motion were also introduced. These physical quantities and parameters were compared between the dominant and non-dominant hands. The ball-throwing distances in the trained and untrained groups were 2.58 and 1.73 times higher for the dominant hand than for the non-dominant hand, respectively. The difference in these values for both the hands of the switch thrower, however, were very small. The throwing time, moving time, and mean ball velocity in the back-swing phase in the trained group were 1.16, 1.65 and 1.35 times higher for the dominant hand than for the non-dominant hand, respectively. These phenomena were not observed in the untrained group and the switch thrower. The mean ball velocities in the acceleration phase for the trained and untrained groups were 2.0 and 1.5 times higher for the dominant hand than for the non-dominant hand, respectively. These values were more highly correlated with the ball-throwing distance in the trained group than in the untrained group. Significant correlations between seven parameters and ball-throwing distance were all observed for the dominant hand. However, only three of these parameters showed significant correlations for the non-dominant hand. These results show that the relationship between ball-throwing distance and throwing motion is closer for the dominant hand than for the non-dominant hand. In the present paper, possible roles of the dominant and non-dominant hands in the relationship between throwing motion and ball-throwing distance are also discussed.