The role of cavitation nuclei on sheet cavitation inception was investigated experimentally for three axisymmetric test bodies, by using a nuclei generator. With no added nuclei, the incipient cavitation number σ _i showed a large scattering, whereas, when nuclei were added, the scattering became fairly small and σ _i converged to the upper limit of σ _i with no added nuclei. It also coincided with the desinent cavitation number σ _d . By using Laser Doppler Velocimeter, the velocity distribution on axisymmetric bodies were measured, and good agreement was obtained with calculated results. The pressure coefficient at separation point c_ps was also measured by LDV and was compared with σ _i , which confirmed the result obtained by Casey that σ _i is equal to, or slightly less than (- c_ps ). A hypothesis for the mechanism of sheet cavity inception was made, taking account of the surface tension of nuclei and the pressure fluctuation at the reattachment zone of a separated flow. It explained, at least qualitatively, the dependence of σ _i on u _∞ and the relation between σ _i and (- c_ps ). By controlling the amount of added nuclei, the radius of nuclei which contribute to the sheet cavity inception was estimated to be about 20μm.