Layered niobate oxide (K4Nb6O17.3H(2)O) films With high orientation and strong adhesion were fabricated by electrophoretic deposition. The deposited films displayed the behavior of a typical n-type semiconductor in K2SO4 solution. When the films were irradiated with UV light, an anodic photocurrent due to the oxidative reaction of the water between the NbO6 layers could be observed. Consequently, the deposited film was converted by photoelectrochemical oxidation from a hydrated form (K4Nb6O17.3H(2)O) into an anhydrous form (K4Nb6O17).