An experimental study was carried out on the transient behavior of a cavitating centrifugal pump during sudden opening or closure of the discharge valve. The experimental results indicate that the transient performance of the pump with cavitation shows a rather different change from the quasi-steady one. Moreover, it was established that a rapid change in boundary condition results in low-cycle pressure oscillation, the ocurrence of which depends on the speed of valve opening/closure and suction pressure, and is nearly independent of pipe length. The frequency of pressure oscilation was found to be related to the pipe length only for valve closure.