Single-layered g-C3N4 nanosheets have been fabricated by delaminating directly its bulk counterpart in an alkaline solution. According to the theoretical modeling, the interaction of OH- with terminal -NH2 or bridged -NH- group of the triazine units within bulk g-C3N4 crystal structure could result in decreased bonding energy between layers and promote the total delamination. The resulting g-C3N4 nanosheets colloid has a relatively high concentration (12 g/L.) compared with the traditional ultrasonic assistant exfoliation method. The delaminated nanosheets are revealed by atomic force microscopy to show a lateral size of a hundred nanometers and a thickness of about 0.4 nm, which provides a direct evidence for the total exfoliation of g-C3N4 crystals into their single sheets. More importantly, the X-ray diffraction measurement confirms that the g-C3N4 nanosheets could be re-assembled with well-preserved original crystal structure. The exfoliation mechanism was also confirmed by the DFT calculation. (C) 2017 Elsevier Inc. All rights reserved.