Interface of the Group X metal oxides and TiO2 nanostructure has been examined regarding the photoelectrochemical water splitting reaction. Deposition of NiO-only nanoparticles covered the rutile (110) side of TiO2 nanostructure. However, application of the Group X hetero-metal oxides somewhat opened the rutile (110) side. Thermal post-treatment of the hetero-metal oxides at medium temperature readily generated mixed valence states of a metallic site and the high oxidation states on the TiO2-Group X hetero-metal oxides interface. The thermal post-treatment simultaneously generated the both catalytic sites for water splitting reactions, of which surface successfully facilitated the photoelectrochemical water splitting in the absence of a redox mediator. In addition to the formation of p-n heterojunction, the co-existing catalytic sites surely promoted the overall water splitting. The TiO2 surface decoration with the Group X hetero-metal oxides modulates band structure, as well provides an effective method to control the surface charge recombination. The size controlled TiO2 nanostructure and its surface decoration by the Group X hetero-metal oxides provided beneficial pathways for both of the photo-generated electrons and holes. In this talk, I will discuss the synthetic methods and analytical data for the photoelectrode materials.