Aims: Purple sweet potato (PSP) pigments were proved to protect murine thymocytes from 60Co '-ray-induced mitochondria-mediated apoptosis in our previous study. In this study, we further investigated the effect of PSP pigments on apoptosis related ROS, p53 and Bcl-2 family. Methods: Cell viability was analyzed by MTT. Apoptosis was certified by DNA ladder detection. Reactive oxygen species (ROS) were detected using 2',7',- dichlorofluorescein diacetate (DCFH-DA) probe. P53, Bcl-2 and Bax proteins were analyzed by western blot. The activities of caspase-3 and caspase-9 were determined by fluorogenic substrates detection. Results: PSP pigments treatment prior to 4Gy 60Co '-ray irradiation increased the cell viability and decrease the apoptosis. In the presence of PSP pigments, ROS was scavenged and followed by a p53-depression. A shift in Bcl-2/Bax ratio towards anti-apoptosis was observed as a result of p53-depression. The activities of caspase-9 and caspase-3 were reduced by PSP pigments pretreatment. Conclusions: PSP pigments have a cytoprotective activity against ' radiation. The protective effect of PSP pigments may be involving ROS scavenging, p53 depression and Bcl-2/Bax modulation in a caspase-dependent mitochondrial way.