Molybdenum sulfide (MoS2) has received tremendous attracts for its promising performance in the aspects of hydrogen evolution reaction (HER). To improve the HER activity of MoS2, we designed a flower-shaped CoS2/MoS2 nanocomposite with enhanced HER electroactivity compared with MoS2 nanosheets by a simple one-step hydrothermal method. The facile approach brings about distinct transformation of the morphology from nano sheets to nanoflower structures. The introduction of Co element into MoS2 results in the larger active surface area, more edge-terminated structures, and higher conductivity of the CoS2/MoS2 nanocomposite, which are good for improving the HER electroactivity. In brief, the optimized catalyst exhibits the low overpotential of 154 mV at 10 mA cm(-2), small Tafel slope of 61 mV dec(-1), and excellent stability in acidic solution. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.