The band structures of semiconductor photocatalysts fundamentally determine the photocatalytic activity and the H-2 production from the visible-light-driven water-splitting reaction. We synthesize a suite of multicomponent sulfide photocatalysts, (CuAg)(x)In2xZn2(1-2x)S2 (0x0.5), with tunable band gaps and small crystallite sizes to produce H-2 using visible-light irradiation. The band gap of the photocatalysts decreases from 3.47eV to 1.51eV with the increasing x value. The (CuAg)(0.15)In0.3Zn1.4S2 (x=0.15) photocatalyst yielded the highest photocatalytic activity for H-2 production owing to the broad visible-light absorption range and suitable conduction band potential. Under the optimized reaction conditions, the highest H-2 production rate is 230 mu molm(-2)h(-1) with a visible-light irradiation of 2.7x10(-5) einstein cm(-2)s(-1), and the quantum yield reaches 12.8% at 420 +/- 5nm within 24h. Furthermore, the photocatalytic H-2 production is shown to strongly depend on their band structures, which vary with the elemental ratios and could be analyzed by the Nernst relation. Copyright (c) 2014 John Wiley & Sons, Ltd.