Molybdenum disulfide (MoS2) has become a promising electrochemical catalyst for reduction of protons to hydrogen in the so-called hydrogen evolution reaction (HER). In order to increase the HER activity, a huge effort has been made to design MoS2 catalysts with affording more active sites and higher conductivity. In this paper, an efficient HER electrochemical catalyst has been developed through an in-situ reduction of ammonium tetrathiomolybdate (ATM) on carbon fibers (CFs) to afford layer-expanded MoS2/CFs composites (LE-MoS2/CFs). X-ray diffraction (XRD) indicates the interlayer of MoS2 nano sheets was expanded with d spacing 9.9 angstrom, and transmission electron microscopy (TEM) shows the lattice distance as 0.99 nm, which is agreed with XRD data. The HER test shows that the LE-MoS2/CFs with Mo/C molar ratio of 0.04 has the highest catalytic activity with the lowest overpotential (131 mV vs. RHE) and the highest current density (10 mA cm(-2) at 200 mV vs. RHE), owing to a balance between the numbers of exposed active edge sites of MoS2 and fast transport paths for electrons provided by CFs. (C) 2016 Elsevier B.V. All rights reserved.