This paper presents characteristics of fluidborne noise generated by an axial piston pump. In this analysis, a flow ripple due to compressibility of fluid is considered, in addition to one due to pumping mechanism. The ripple due to compressibility is caused by an unsteady internal leakage which flows backward intermittently, at the neighbourhood of bottom dead center, from the delivery chamber into the cylinder chamber. Since a steady and continuous leakage of piston pump is generally very little, only a capacitant type impedance due to compressibility of fluid in the delivery chamber is considered as pump source impedance. Experimental values of pressure ripple almost agree, up to about 10th harmonic, with calculated values based on foregoing mathematical models for flow ripple and source impedance. It is concluded that the flow ripple of piston pump is mostly due to fluid compressibility, and that the well-known effect of pumping mechanism on the flow ripple can almost be ignored in the case of a relatively high operating pressure.