Photocatalytic overall water splitting has been studied as a potential technique for H₂ production by photon energy conversion. It is important to develop visible-light-driven photocatalysts in terms of utilization of the solar energy. Recently, it was reported that overall water splitting under visible light irradiation proceeded for using two-step photoexcitation systems (Z-scheme). The Z-scheme photocatalysis system is composed of two kinds of photocatalysts and a reversible redox couple. Thus, the development of redox couples in the Z-scheme photocatalysis systems is important. In the present study, we studied to construct a visible-light-driven Z-scheme photocatalysis system using Co-complexes, [Co(phen)₃]²⁺ and [Co(bpy)₃]²⁺, as redox couples. Rh-doped SrTiO₃ (denoted as SrTiO₃:Rh) powder for the H₂ evolution photocatalyst was prepared by a solid state reaction. A Ru cocatalyst was loaded on SrTiO₃:Rh by photodeposition. BiVO₄ powder for the O₂ evolution photocatalyst was prepared by a liquid-solid-reaction. [Co(phen)₃]^3+/2+ and [Co(bpy)₃]^3+/2+ redox couples worked as electron mediators for overall water splitting by the Z-scheme photocatalysis system, (Ru/SrTiO₃:Rh)-(BiVO₄). The photocatalytic activity depended on pH. The pH dependence is due to the change in potential differences between band positions of SrTiO₃:Rh and BiVO₄ photocatalysts, and redox potential of the Co-complexes. In conclusion, we succeeded in the construction of the new Z-scheme systems for overall water splitting under visible light irradiation.