Amorphous molybdenum sulfide (MoSx) has attracted great attention as an alternative catalyst of platinum for electrochemical hydrogen evolution reaction (HER). In order to investigate the effect of oxygen incorporation in the MoSx catalyst, oxygen-incorporated MoOxSy catalysts with various oxygen contents were prepared on carbon fiber papers (CFPs) by chemical bath deposition. The oxygen content and chemical states of MoOxSy catalysts were controlled by adjusting the reducing agent concentration of Na2S2O4 in order to reveal the relation between chemical states and HER performance. Compared to oxygen-free MoSx catalysts, the oxygen-incorporated MoOxSy catalysts exhibit more excellent activity for HER. One of the MoOxSy catalysts requires an overpotential of 164 mV to reach a cathodic current density of 10 mA/cm(2) with a Tafel slope of 43 mV/dec representing the Volmer-Heyrovsky mechanism. The high performance is attributed to enhanced activity and/or higher electrical conductivity due to the presence of Mo5+ state in the MoOxSy catalysts.