Zinc orthogermanate was prepared via a hydrothermal method and a remarkable synergistic effect on the photocatalytic activity for overall water splitting was found for Zn2GeO4 co-loaded with noble metals (Pt, Rh, Pd, Au) and metal oxides (RuO2, IrO2). The photocatalytic activity of Pt-RuO2/Zn2GeO4 for overall water splitting is 2.2 times of Pt/Zn2GeO4 and 3.3 times of RuO2/Zn2GeO4. Photocatalytic half reactions evaluation of water splitting for H-2 and O-2 productions shows that Pt plays the major roles in H-2 production and RuO2 promotes the O-2 production. The roles and valence states of co-catalysts and the mechanism of photocatalytic reaction are discussed.