An efficient Mo-doped BiVO4 photoelectrode for water oxidation was easily prepared from a Bi-, V-, and Mo-containing aqueous precursor solution. The thickness of BiVO4 films was controllable by changing the volume of the precursor solution, giving a transparent BiVO4 film with a thickness of 130-260 nm. The Mo-doped BiVO4 photoelectrodes showed higher photocurrents than a non-doped BiVO4 photoelectrode prepared by the same procedure. An incident photon-to-current efficacy (IPCE) of the Mo-doped BiVO4 electrode with CoOx surface modification reached 33% at 1.23V vs. RHE at 420 nm.