Natural and ventilated cavitations generated on a smooth-nosed axisymmetric body were studied experimental-ly. The characteristics of small scale and localized fluctuations of "steady cavities" were measured by pressure transducers. Comparisons between natural and ventilated cavities at differ-ent measured points for several cavitation numbers were done. It was observed that the dominant fluctuations were concen-trated in the frequency range of OHz-50Hz for all the cavitati-on cases, Similar shapes and magnitudes of the frequency spectra were detected for both natural and ventilated cavities. Much larger spectral amplitude in the cavity closure region suggested as fluctuations source. From partial cavitating flow to supercavitating flow, the dominat frequency and the corre-sponding amplitude decreased with decrasing cavitation num-ber, which meant that cavity became more steady while devel-oping.