TiO2/g-C3N4 2D/2D heterojunction nanocomposites were successfully synthesized through a facile self-assembly method. The structure characterization results shows good interaction between TiO2 nanosheets and g-C3N4 nanosheets. The photocatalytic activity of TiO2/g-C3N4 samples were measured by hydrogen production in water splitting under visible light irradiation, which was found that the composites enhance the photocatalytic activity clearly compared to pure g-C3N4 and TiO2 nanosheets. The results could attribute to the formation of 2D heterojunction because of the stimulative charge transfer, promotional separation efficiency of photoexcited electron and hole and the suitable band positions. Besides, the samples exhibited substantial stability under visible light irradiation by the recycling experiments. The feasible photocatalytic mechanism was minutely discussed, which could explain the enhanced photocatalytic activity. [GRAPHICS] .