This study examined two factors that are important for baseball batting, (1) swing speed and (2) ability to repeat the same swing (repeatability). Twenty male subjects participated in the study; eight beginners, five active players from a university baseball club (players), and another seven who played baseball at a high school or university but are not active now (experienced). Each subject hit a ball on a batting tee fifteen times. Swing speed was measured by a custom-made machine using laser position detectors. The motion of the bat head was also recorded by a high speed video camera (250 flames/s). Swing speed was 82.6km/h, 108.2km/h, and 97.2km/h, for the beginner, player, and experienced groups, respectively. Repeatability of the swing was evaluated by utilizing the standard deviation (SD) of the bat head position in the vertical plane when it hit the ball. The SD was 2.1cm for the beginners and 1.1 cm for the player and experienced groups. There were significant differences in both swing speed and repeatability between the beginners and the player or experienced groups. These data suggest that both swing speed and repeatability improve with practice.