Porous structured Ag-Ag2S/MoS2 composite was synthesized by a facile chemical etching method and tested with respect to its application in hydrogen evolution reaction (HER). Extensive spectroscopic and electrochemical characterizations were performed to investigate the origin of the catalytic activity of this Ag-Ag2S/MoS2 composite and understand the property of this material for HER. During the synthesis process, cysteine (Cys) was used to improve the number of highly catalytic S edges as revealed by a low ratio of Mo to S. The high density of active sites that result from the rough and porous structure surface morphology also contributes to the highly catalytic activity. The catalytic activity for HER increases with the change of material morphology from a relatively complete lamellar structure to the porous structure. The electrochemical stability tests indicate that the catalyst remains highly active throughout prolonged operation. Our enhanced understanding of this highly active hydrogen evolution catalyst may facilitate the development of economical electrochemical hydrogen production systems. (C) 2014 Published by Elsevier Ltd.