The effect of heating time on the polymerization processes of urea into g-C3N4 nanosheets was studied in Ar atmosphere. It was found that heating time had a great influence on the crystalline quality, specific surface area (S-BET) and photocatalytic H-2 production of the obtained g-C3N4 nanosheets. G-C3N4 nanosheets with some degree of disorders in crystal structure were formed within 1 h at 550 degrees C, and these structural disorders maintained after 4 h, however disorders disappeared after extended heating of 6 h. G-C3N4 nanosheets with similar disorders in the crystal structure hold similar SBET and exhibit comparable H-2 production rates. The highest H-2 production rate of 1.4 mmol h(-1) g(-1) occurs after 8 h heating, corresponding to 2.6% quantum efficiency at 420 nm. Copyright (C) 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.