A molecular Keggin polyoxometalate catalyst K-7[(CoCoII)-Co-III(H2O)W11O39](1) was successfully synthesized and efficiently catalyzed the hydrogen evolution. To the best of our knowledge, the molecular Keggin polyoxometalate catalyst 1 is the first reported polyoxometalate containing cobalt with efficient hydrogen production activity under the visible light irradiation. Under the optimal photocatalytic condition (photoirradiation at lambda >= 420 nm, Eosin-Y as the photosensitizer, triethanolamine as the electron donor and Pt produced in situ photoreduction as co-catalyst), the turnover number (TON/based on catalyst) reached as high as 100; the initial quantum yield and the initial turnover frequency (TOP) at the first 10 min were 29% and 0.025 s(-1), respectively. The hydrogen evolution average rate of 1 achieved 13,395 mu mol h(-1) g(-1), as far as we are concerned, which is the highest among all the polyoxometalates photocatalytic systems reported so far. A possible mechanism of the hydrogen evolution reaction was proposed on the basis of steady-state fluorescence decay studies. Copyright (C) 2014, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.