For the first time, the interwoven CoSe2/CNTs hybrid with ultra-small CoSe2 nanoparticles on highly conductive CNTs has been synthesized by a facile one-pot hydrothermal method. The CoSe2/CNTs hybrid has been investigated as electrocatalysts for the Hydrogen evolution reaction (HER) in acidic media. The physicochemical characterizations of CoSe2/CNTs have been performed by X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The HER performances have been evaluated by linear sweep voltammetry (LSV), cyclic voltammetry (CV), chronoamperometry, and electrochemical impedance spectroscopy (EIS). The CNT content in the CoSe2/CNTs hybrids has been optimized and CoSe2/CNTs (14.7 wt%) exhibits the best HER performance. It delivers a very small Tafel slope of -32 mV/dec,a low onset potential of -150 mV vs RHE and overpotential of -186 mV at -10 mA/cm(2), which are much better than those of bare CoSe2 with a Tafel slope of -52 mV/dec, an onset potential of -234 mV vs RHE and overpotential of -293 mV vs RHE at -10 mA/cm(2). Furthermore, the CoSe2/CNTs hybrid also demonstrates good long-term stability even after 1000 cycles. The excellent HER performance of CoSe2/CNTs can be attributed to its unique and conductive interwoven structure. This work provides insights into rational design and facile synthesis of non-precious electrocatalysts with high efficiency and good stability for HER. (C) 2017 Elsevier Ltd. All rights reserved.