This paper describes the dynamic characteristics of a centrifugal blood pump with hydrodynamic levitating bearings. Flow fluctuations were realized from 0.25 to 3.0 Hz by an oscillator driver in the fluid circulatory system for the test pump with conical spiral groove bearings. The stability test was done for the whirling motion of impeller and the pump stability was discussed based on the dynamic tests under sinusoidal change in flow rate. The measured impeller whirling motions were found to be stable, and the response of pump total pressure rise to flow rate change was also stable for the test pump.