Graphitic carbon nitride (g-C3N4) is a promising visible-light-driven photocatalyst for solar energy conversion by splitting water into H-2. However, the photocatalytic performance of g-C3N4 is not sufficient because of low surface area and fast recombination of charge carriers. Here, g-C3N4 with nanosheet structure was prepared by using mixture of melamine (M) and urea (U) as the precursors for the photocatalytic H-2 production from water. The use of U increased the surface area with mesoporous structure and defects of nitrogen vacancies acting as trap states in g-C3N4. The as-obtained g-C3N4-M1U2 (1 and 2 denote the weight ratios of M and U, respectively) exhibited the photocatalytic H-2 production rate of 3.1 mmol g(-1) h(-1) under lambda >= 400 nm light irradiation and apparent quantum efficiency (AQE) of 74% at lambda = 400 nm. Single-particle photoluminescence (PL), originated from charge recombination of photogenerated charge carriers, showed longer lifetime of charge carriers in g-C3N4-M1U2 than that in g-C3N4-M. Femtosecond time-resolved diffuse reflectance measurement was performed to observe the photogenerated electrons trapping in g-C3N4-MxUy. The results show that the electron trapping by the defects as trap states occurs faster in g-C3N4-MxUy than in g-C3N4-M. It is suggested that the use of U increases the defects as electron trap states, leading efficient photocatalytic H-2 production.