Herein, the structural effect of MoS2 as a cocatalyst of photocatalytic H-2 generation activity of g-C3N4 under visible light irradiation is studied. By using single-particle photoluminescence (PL) and femtosecond time-resolved transient absorption spectroscopies, charge transfer kinetics between g-C3N4 and two kinds of nanostructured MoS2 (nanodot and monolayer) are systematically investigated. Single-particle PL results show the emission of g-C3N4 is quenched by MoS2 nanodots more effectively than MoS2 monolayers. Electron injection rate and efficiency of g-C3N4/MoS2-nanodot hybrid are calculated to be 5.96 x 10(9) s(-1) and 73.3%, respectively, from transient absorption spectral measurement, which are 4.8 times faster and 2.0 times higher than those of g-C3N4/MoS2-monolayer hybrid. Stronger intimate junction between MoS2 nanodots and g-C3N4 is suggested to be responsible for faster and more efficient electron injection. In addition, more unsaturated terminal sulfur atoms can serve as the active site in MoS2 nanodot compared with MoS2 monolayer. Therefore, g-C3N4/MoS2 nanodot exhibits a 7.9 times higher photocatalytic activity for H-2 evolution (660 mu mol g-(1) h(-1)) than g-C3N4/MoS2 monolayer (83.8 mu mol g(-1) h(-1)). This work provides deep insight into charge transfer between g-C3N4 and nanostructured MoS2 cocatalysts, which can open a new avenue for more rationally designing MoS2-based catalysts for H-2 evolution.