Activating the inert basal planes of layered molybdenum disulfide (MoS2) is critical to deliver its high hydrogen evolution reaction (HER) efficiency. Herein, oxygen-incorparated MoSx with abundant undercoordinated Mo atoms is fabricated by a facile solvothermal procedure, which realizes synergistically structural and electronic regulations of MoS2 inert basal planes. Experiment results reveal that oxygen incoparation can effectively modulate the electronic structure and further optimize the intrinsic conductivity, while the defect-rich structure with abundant undercoordinated Mo atoms increases the number of active sites. Moreover, the influence of solvothermal temperature on activity of MoS2-x is also investigated. The achieved MoSx electrocatalyst prepared at 220 degrees C exhibits a superior activity for HER with a low overpotential of 191 mV at 10 mA cm(-2), a small Tafel slope of 67 mV dec(-1), and an excellent stability due to the largest surface area and superior conductivity. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.