A facile two-step hydrothermal approach is adopted to synthesize MoSe2/N-doped RGO (NG) composites with the N/C atomic percentage changing from 1.13 to 5.16 at%. In the composites, nanoclusters of MoSe2 nanosheets are dispersed on plicated NG nanosheets. The electrochemical measurement suggests that the MoSe2/NG composites exhibit enhanced electro-catalytic HER activity as compared to MoSe2 and MoSe2/RGO. Moreover, as the N/C ratio of NG is increased, the activity of MoSe2/NG increases firstly and then decreases. At low N/C ratio, the impact of interfacial energy barrier between MoSe2 and NG is negligible and the electron transfer is substantial, so the activity of the MoSe2/NG composites increases with carrier concentration in NG. However, at high N/C ratio, the energy barrier blocks the electron transfer from NG to MoSe2 remarkably. Consequently, the MoSe2/NG composites with an intermediate N/C ratio have the highest activity. Owing to the synergistic effect of NG and MoSe2, the Tafel slope of the composites is reduced from 114.69 to 78.45 mV dec(-1) by 32% as compared to pure MoSe2. The results provide us valuable information for efficient design of transition metal dichalcogenide catalysts for electro-catalytic hydrogen evolution.