A noble-metal-free photocatalytic system for highly efficient hydrogen production has been developed with colloidal nickel nanoparticles (Ni NPs), CdS nanorods (CdS NRs) and lactic acid (LA) as catalyst, photosensitizer and sacrificial electron donor, respectively, in aqueous solution without any organic solvent. The hydrogen evolution activity of the highly active Ni NPs (6 nm) could amount to 80% of the well-known Pt nanoparticles (5 nm) in equimolar amount at pH 3.0 water solution under visible light (λ ≥ 420 nm) irradiation. A maximum turnover number (TON) of 9710 based on Ni NPs (6 nm) was obtained after 10 h of irradiation at a catalyst concentration of 1.38 × 10⁻⁵ M and turnover frequency (TOF) value of 1232 was achieved for the first 6 h of photocatalytic reaction. A series of Ni nanoparticles colloids with different sizes plus Fe, Co nanoparticles were also tested for photocatalytic H₂-evolution. The results showed the obvious effect of Ni NPs size on the hydrogen evolution activity and the smaller (6 nm) Ni nanoparticles exhibited the highest activity compared with other nanoparticles of 11 nm and 20 nm in size. This work demonstrates the size control of non-precious metal nanoparticles could effectively enhance the photocatalytic hydrogen production, which provides an inexpensive means of developing efficient and low-cost photocatalytic systems for harnessing solar energy.