Ultrathin two-dimensional (2D) g-C3N4 nanosheets (UCNS) are facilely prepared by liquid-exfoliation of the urea-derived g-C3N4 via an HCl-assisted hydrothermal treatment method. The UCNS are served as the novel visible-light-driven photocatalyst to degrade a typical organic pollutant, p-nitrophenol (PNP), in an aqueous solution. By the combination of the advantages of plentiful exposed active sites, fast photogenerated charge carrier separation rate, aligned energy levels and easy dispersion in an aqueous solution, the UCNS exhibit considerably enhanced visible-light photocatalytic activity toward the degradation of the target compound in comparison of their bulk g-C3N4 counterpart, melamine-derived g-C3N4 nanoparticles or Degussa P25 TiO2. The indirect chemical probe experimental results indicate that both the superoxide radicals and the photogenerated holes are responsible for the complete decomposition of PNP. Additionally, the UCNS can be reused at least four times without obvious activity loss and morphology change, exhibiting the excellent reusability in photodegradation aqueous organic pollutants. (C) 2017 Elsevier B.V. All rights reserved.