Various thin films for photoelectrochemical (PEC) water splitting were prepared and their PEC performance was tested. The precursor solutions for WO3 and BiVO4 photocatalysts were synthesized by solution processes, and the graphene oxide (GO) was prepared by Tour’s method and was calcined and converted to reduced graphene oxide (rGO). The composite photocatalyst thin films of WO3, BiVO4, WO3/BiVO4 and WO3/BiVO4-rGO were prepared on fluorine doped tin oxide glass by spin coating and calcination processes and the PEC performances were analyzed for those photocatalyst layers. The controlled WO3/BiVO4 heterojunction layer showed better PEC performance than the WO3 or BiVO4 single layer by the combined effects of photocatalysts. The WO3/BiVO4-rGO film with the optimum concentration of rGO showed a noticeable increase in photocurrent density because of the increased electrical conductivity by rGO and reduced recombination rate in BiVO4 layer.