Ni(OH)2-modified graphitic carbon nitride (Ni(OH)2–g-C3N4) composite photocatalysts were prepared by a simple precipitation method using g-C3N4 as support and nickel nitrate as precursor. The effect of Ni(OH)2 content on the rate of visible-light photocatalytic H2-production was studied for a series of Ni(OH)2–g-C3N4 composite samples in triethanolamine aqueous solutions. The results demonstrated that Ni(OH)2 was an efficient co-catalyst for the photocatalytic H2 production of g-C3N4. The optimal Ni(OH)2 loading was found to be 0.5 mol%, giving a H2-production rate of 7.6 μmol h−1 (with an apparent quantum efficiency (QE) of 1.1% at 420 nm), which approached that of optimal 1.0 wt% Pt/g-C3N4 (8.2 μmol h−1). This work showed the possibility for the utilization of low cost Ni(OH)2 as a substitute for noble metals (such as Pt) in the photocatalytic H2 production for g-C3N4.