Photocatalytic water splitting is an environmentally friendly technique for sustainable solar hydrogen production, which requires low-cost and earth-abundant co-catalysts to replace expensive noble metal such as platinum. Herein, for the first time, we demonstrate noble-metal-free Ni-Mo alloys which has been widely attended in the field of electrocatalysis as co-catalysts to drastically enhance the activity of g-C3N4 visible light photocatalyst for H-2 production from water. The novel Ni-Mo/g-C3N4 photocatalyst is in-situ synthesized by an effective and simple one-pot synthesis method. For the synthesized Ni0.4Mo0.6 and with optimized content of 10 wt%, composite photocatalyst Ni0.4Mo0.6/g-C3N4 shows the champion photocatalytic H-2 generation rate 1785 mu mol g(-1) h(-1), which is about 37 times higher than that of pure g-C3N4, and comparable to that of the optimized Pt/g-C3N4. Based on the detailed analyses of UV-vis diffuse reflectance spectroscopy, photoluminescence spectra, photocurrent response curves and electrochemical impedance spectroscopy Nyquist plots, the present good efficiency of Ni-Mo/g-C3N4 is mainly attributed to the presence of Ni-Mo alloys, which effectively promote the separation and suppress the recombination of photogenerated electrons and holes.