We demonstrated the precise motion of a nanoliter-volume oil droplet in a capillary tube by using a flexural acoustic wave. An acoustic standing wave was excited between a compact co-axial acoustic transducer and the free end of the capillary tube. The liquid droplet was trapped at an antinode of the standing wave thus, the position of the droplet could be controlled by tuning the positions of the acoustic antinodes or the acoustic frequency. The position control was achieved over the entire length (15 cm) of the acoustic interaction region of the capillary tube to a precision of a few tens of m.