Abstract: Objective：To compare the reactive oxygen species (ROS) levels in young and aged bone marrow mesenchymal stem cells(BMSCs), explore whether redundant reactive oxygen species (ROS) inhibits osteogenic differentiation of aged BMSCs, and investigate the mechanism of ROS enhancement. Methods：Osteogenic differentiation of BMSCs was confirmed by ALP staining and realtime RT-PCR. Fluorescence analysis and Flow cytometry were performed to detect ROS levels. Realtime RT-PCR was performed to measure superoxide dismutase 2(SOD2) and catalase(CAT) expression. Results：Osteogenic differentiation of aged BMSCs was significantly decreased compared to young BMSCs. Redundant ROS inhibited osteogenic differentiation of aged BMSCs. ROS levels in aged BMSCs were enhanced by dysfunction of SOD2 and CAT. Conclusions：Dysfunction of enzymatic antioxidant system leads to oxidative damage, which inhibits osteogenic differentiation of aged BMSCs.