If a pipe end is faced at an ultrasonic vibrating surface with a small gap in the liquid, the liquid is sucked into the pipe. The ultrasonic pump under our investigation is based on this phenomenon. In the first part of this paper, we explore the relationships between the number of pipes and the pump characteristics. The flow rate is improved proportionally to the number of pipes if a piston-vibrating surface is used, whereas the maximum flow rate is improved by a factor of only 1.5 using two pipes if a bending vibrator is employed. Second, we research how the inner diameter of the pipe affects the flow rate. The maximum flow rate is improved by a factor of 1.9 if the inner diameter is changed from 3.5 to 5.0 mm.