Contact swimming behavior among the wild Indo-Pacific bottlenose dolphins (Tursiops aduncus) of Mikura Island, Japan, was quantitatively analyzed. This behavior occurred between two individuals during pair swimming. One dolphin (toucher) used the front side of its pectoral fin to touch another dolphin (receiver) mainly on the lateral side (80.7 %). In most of all episodes, the distance between the two dolphins during contact swimming behavior was 1 body width, 0.25 body length and 0.5 to 1 body height. The toucher tended to swim behind the receiver in 92% of all episodes. The duration of contact swimming episodes ranged from 1-48 s with an average (+/- SD) of 6.3 +/- 9.4 s. There were no cases of the toucher and the receiver switching roles during a contact swimming episode. The swimming partners in this behavior were mainly mother-calf and female-female pairs. Contact swimming behavior tended to be initiated and ended by the toucher. In most cases, the receiver was the one who first changed speed and direction during contact swimming. In some cases, it could be clearly seen that the stroke frequency of the receiver was higher than that of the toucher. The results suggest that contact swimming behavior was leaded by the receiver and likely benefits the toucher.Several possible functions of this behavior were discussed.