The underwater oil wettability of a flat Nb2O5 photocatalyst surface prepared by a sol-gel based method was investigated. The Nb2O5 surface exhibited photocatalytic oxidation and photo-induced superhydrophilic properties under UV irradiation, and its activity was comparable to those of anatase-type TiO2 surfaces prepared by a sol-gel based method. The surface exhibited excellent underwater superoleophobicity toward n-hexadecane and oleic acid. The underwater oil repellency was superior to that of the TiO2 surface.