Two-dimensional (2D) MoS2 has been considered as a potential catalyst in hydrogen evolution reaction (HER), but its catalytic reactions usually only occur at the active edge sites rather than the inert surfaces. In this work, we propose a strategy to enhance the catalytic activity of MoS2 by decorating the inert surfaces of MoS2 nanosheets with ultrafine Pt nanoparticles through an atomic layer deposition (ALD) technique. The optimized Pt/MoS2 catalyst with ultralow Pt mass loading (similar to 2.2 wt%) presents exceptional HER performances in terms of low onset overpotential (31 mV), small Tafel slope (52 mV dec (1)) and firm HER durability, which is comparable to the commercial Pt/C catalyst. (C) 2017 Elsevier Ltd. All rights reserved.