Ultra-high-density rhenium diselenide (ReSe2) nanoflakes were synthesized on a porous carbon cloth (PCC) by chemical vapor deposition (CVD). Besides the two-dimensional/three-dimensional (2D/3D) construction with more active catalytic sites, the small size effect together with the interfacial C-Se bonding facilitated the electron transport between ReSe2 and PCC. Hence, the heat-treated ReSe2@PCC with enhanced charge transport is by far the best performance electrode for the hydrogen evolution reaction (HER) among the state-of-the-art ReX2-based electrodes.