A dinuclear cobalt complex Co2(OH)L1(ClO4)3 (1, L1=N(CH2)2NHCH2(m‐C6H4)CH2NH(CH2)23N) displays high selectivity and efficiency for the photocatalytic reduction of CO2 to CO in CH3CN/H2O (v/v=4:1) under a 450 nm LED light irradiation, with a light intensity of 100 mW cm−2. The selectivity reaches as high as 98 %, and the turnover numbers (TON) and turnover frequencies (TOF) reach as high as 16896 and 0.47 s−1, respectively, with the calculated quantum yield of 0.04 %. Such high activity can be attributed to the synergistic catalysis effect between two CoII ions within 1, which is strongly supported by the results of control experiments and DFT calculations. CoCo catalysts: A dinuclear cobalt cryptate displays high selectivity and efficiency for the photocatalytic reduction of CO2 to CO in CH3CN/H2O solution under a 450 nm LED light irradiation, at a light intensity of 100 mW cm−2. The high catalytic efficiency originates from the synergistic catalysis effect between two CoII ions within the catalyst.