Zn2GeO4 and Zn2GeO4:Mn2+ were synthesized by a hydrothermal method. The phase, microstructure, and optical and photoelectrochemical properties were investigated. The photocatalytic activities were evaluated by the photocatalytic hydrogen generation. The X-ray diffraction (XRD), scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) results indicate the Mn2+ doping has no obvious influence on the phase and microstructure of Zn2GeO4. But the Mn2+ doping influences the optical and photoelectrochemical properties obviously. The Mn2+ doping leads to the red shift of band gap edge and the light absorption in visible region. The Zn2GeO4:Mn2+ has the greater light absorption efficiency, more efficient e(-)-h(+) pair separation and promoting charge transfer across the electrode/electrolyte interface. These characteristics of Zn2GeO4:Mn2+ suggest that it has higher activity than that of Zn2GeO4 and this is confirmed by the highly efficient hydrogen generation.