The photoinduced hydrophilicity of SrTiO3 single crystals with (100), (110), and (111) facets was investigated. The (100) and (111) facets had a higher hydrophilic conversion rate under UV irradiation than the (110) facet. This is attributed to an unstable O atom on the surface of the (100) and (111) facets. The crystal-face dependence of the hydrophilic conversion was weakened by repeated UV irradiation, which indicates that an irreversible structural change is caused on the SrTiO3 surface by UV irradiation.