Amorphous MoS2 porous thin films (denoted as MoS2 PTFs) with high activity towards hydrogen evolution reaction (HER) were fabricated by in situ sulfuration of a Mo substrate. A small overpotential (~120 mV) and a low Tafel slope (~41 mV dec(-1)) can be observed and their excellent performance was ascribed to the combination of the amorphous feature, porous structure and optimized thickness.