Molybdenum phosphide (MoP) has attracted a lot of attentions as a potential electrocatalyst for the hydrogen evolution reaction (HER). Although great efforts have been made to improve the HER activity of MoP, the rational design of MoP catalysts with either more active sites or higher conductivity is still challenging. Herein, a defect-rich structure (DR-MoP) is synthesized via a novel and facile low-temperature calcination strategy. Moreover, the DR-MoP is also proved to be incorporated with oxygen. The defect-rich structures could provide more active sites, and the incorporation of oxygen could further enhance the intrinsic conductivity. Thus, the DR-MoP catalyst shows outstanding HER activity and stability in both acidic and alkaline media, making it a good alternative to replace the precious-metal catalysts. Besides, the formation mechanism of DR-MoP has been discussed by controlling different annealing temperatures. This work paves a novel and effective way for improving the HER performance of transition metal phosphides by defect engineering. (c) 2018 Elsevier Ltd. All rights reserved.