In order to research the radio-protective properties of a new antioxidant peptide, SS31 in vitro, cells were irradiated by 60Co γ-rays and incubated with SS31 in different concentration. Cell viability, mitochondrial mem-brane potential, cell living rate and ROS generation were investigated and compared with that of control group. After irradiation with 7.5 Gy γ-rays, SS31 could reduce the cell injury significantly while cell viability decreased and apoptotic rate increased definitely, with higher ROS generation, mitochondrial membrane potential collapsing and cell cycle arrest if without intervention by use of SS31. Compared with the control group, SS31 intervention group showed statistical difference. This study has been revealed that SS31 has potency to reduce acute radiation injury and thereby act as a new radio-protective agent.Cited