g-C3N4 nanosheets with porous structures (labelled PGN) were prepared by an extremely facile one-step, template-free method. The method used to prepare porous g-C3N4 nanosheets in this research was thermal polycondensation of urea pre-treated with ethanol. These nanosheets were compared with g-C3N4 agglomerates (labelled BG) prepared with raw urea. The pre-treatment process did not change the crystal structure of urea but changed the thermal polymerization process of urea to form g-C3N4. The change in the thermal polymerization process resulted in the formation of porous g-C3N4 nanosheets. The as-prepared PGN photocatalyst has an enlarged surface area of 66.0 m(2) g(-1) and a pore volume of 0.357 cm(3) g(-1), leading to enhanced visible light photocatalytic efficiency. The photocatalytic activity of g-C3N4 was evaluated by the photodegradation experiments with methylene blue (MB). The results indicated that PGN exhibited high and stable photocatalytic activity. The effective separation and transmission of photogenerated electron-hole pairs caused by precursor (urea) pre-treatment as well as the large BET surface area are associated with the enhanced photocatalytic activity of PGN.