Ultrathin graphitic carbon nitride (g-C 3 N 4 ) nanosheets were synthesized via thermal exfoliation of bulk urea-derived g-C 3 N 4 under an argon atmosphere. As a visible-light responsive photocatalyst, this material exhibits a much superior photocatalytic activity in pollution degradation and H 2 evolution than bulk g-C 3 N 4 , as a result of the extended region of visible light response and the enhanced surface area of ultrathin g-C 3 N 4 nanosheets. These findings may provide a promising and facile approach to the design of high-performance photocatalysts. Ultrathin graphitic carbon nitride (UGCN) nanosheets with an extended region of visible light response and enhanced surface area were constructed for a significant enhancement in photocatalysis.