The photocatalytic conversion of CO2 to valuable fuels or chemicals has displayed the promise to solve urgent energy and environmental problems. Photocatalytic systems for CO2 reduction in water usually suffer from low efficiency and selectivity due to competitive proton reduction and relatively low CO2 concentration. In this work, we report a CoII−ZnII heterometallic dinuclear complex [CoZn(bpbp)(CH3COO)2](CH3COO) (CoZn), which shows high photocatalytic activity and selectivity for CO2-to-CO conversion in a water/acetonitrile solution. The values of TONCO and CO selectivity reach as high as 6680 and 98%, respectively. It was found that CoZn exhibits much higher activity than the corresponding CoII−CoII homometallic dinuclear complex [Co2(bpbp)(CH3COO)2](CH3COO) (CoCo) under the same conditions. The electrochemical properties and DFT calculations indicated that the improved photocatalytic activity of CoZn in comparison to CoCo is attributed to the smaller energy barrier of the rate-limiting CO2 coordination step for photocatalytic CO2-to-CO conversion via the synergistic effect between the two different metal centers.