Abstract：The purpose of this study was to understand the status of grip and finger force of pitching arm, and to explore the feasibility of different weighted balls for pitching-velocity training among 3 levels (U12, U15, and U18) of young baseball pitchers. Thirty-six pitchers (12 pitchers from each level) were participated in this research. The grip force of pitching arm, finger force (included index and middle fingers) of pitching arm, and ball velocity (included initial velocity, final velocity, and velocity gap) were measured while pitching different weighted baseball (range: 60-170 g). The results showed that the grip force was greater with the level increased, but the finger force was not. The initial velocity of all levels was increased as the weight of the ball decreased. The final velocity of U12 pitchers was not increased due to the limitations of grip force, finger force, and pitching skill, but the final velocity was decreased as the weight of the ball decrease in U15 and U18 pitchers. The velocity gap while pitching the heaviest ball in all levels of pitchers was significantly less than that they pitched the standard-weighted ball, and the velocity gap started to significantly larger than that they pitched the standard-weighted ball when the ball lighter than 80 g (U12 pitchers), 100 g (U15 pitchers), and 110 g (U18 pitchers). We concluded that the injury risk due to fatigue should be noticed when training with weighted ball, and the ball weight that exceeds 170 g should not be used. The underweight ball should not be lighter than 80 g (in U12 level), 100 g (in U15 level), and 110 g (in U18 level) during training sessions, as these weights do not affect the finger movement. Reducing the weight of baseball in U12 level may results in improvement of ball velocity and reduces injury risk at the same time. (Full text)