Ni2+ doped ZnIn2S4 microsphere with flower-like nanoscale petals were prepared by a hydrothermal method. There was an optimal Ni doping content of 0.3 wt% where hydrogen production reached the maximum. Higher Ni2+ doping can hardly dope into the ZnIn2S4 lattice and just stay at ZnIn2S4 surface, leading to decreased activity. It was determined that Ni2+ entering the ZnIn2S4 lattice instead of surface NiS dominated the enhanced photocatalytic activity. The experimental results were rationalized by assuming Ni2+ serving as shallow trapping sites, greatly enhancing the activity of the photocatalyst. N