The ball milling process was adopted to improve the photocatalytic activity of g-C3N4. Sulfur doped g-C3N4, which shows better photoconversion efficiency than pristine g-C3N4, was used as starting material for the modification. The photocatalyst was prepared by calcinating thiourea and the replacement of sulfur with nitrogen was observed. An enhanced dispersion property and enlarged surface area, which can be ascribed to the reduced particle size, were observed after the modification. Furthermore, a reduced recombination rate was measured as a result of the eliminating the amino spices on the surface. The sample modified by for 48 h showed an excellent hydrogen production rate under visible light irradiation with the photocatalytic hydrogen production activity 5.3 times higher than that of the unmodified sample. The prolonged lifetime of the carriers was also identified and the improvement of the photocatalytic activity can be attributed to the synergic effect of the reduced particle size and decreased surface defect concentration. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.