The aim of this study was to investigate the protective effect of hydrogen in a rat model of osteoradionecrosis of the jaw (ORNJ). The rats and bone marrow-derived mesenchymal stem cells (BMSCs) were pre-treated with hydrogen before receiving irradiation (7Gy per fraction, five fractions in total once a day for rats, 4Gy for BMSCs). Reactive oxygen species (ROS) and cell differentiation were measured in the BMSCs. Also, the radioprotective effect of hydrogen for ORNJ in Sprague-Dawley rats was examined by gross clinical manifestations, micro-computed tomography, and histology. Hydrogen significantly reduced the production of ROS in BMSCs after irradiation. The cell viability was significantly decreased after irradiation (P= 0.001), but pre-treatment with hydrogen before irradiation increased the cell viability (P= 0.025). Hydrogen considerably increased the cellular differentiation potential of the irradiated cells. Comparing with the rats underwent irradiaton only, those rats treated by hydrogen-rich saline significantly appeared improved occlusion, salivation, alopecia, oral ulcer, and less bone necrosis. Myofibroblasts accumulated overwhelmingly in the fibrosis medulla and around the sequestrum after irradiation, and this was decreased in the group pre-treated with hydrogen. Hydrogen may represent a strategy for the prevention and treatment of ORNJ. Its high efficacy and low toxicity suggest possible therapeutic application.