Platycodon grandiflorum, Doraji as Korean name, is one of the most widely used traditional oriental medicine for bronchial diseases and also used as a folk remedy for geriatric diseases and inflammatory diseases. In recent studies, it has been reported that some effect of P. grandijlorum is derived from its antioxidant activity, although there is still a lack of evidence to establish its oxy-radical scavenging activity. In this study, total oxy-radical scavenging capacity (TOSC) assay was used to evaluate antioxidant activity of total extracts (T-PG), polysaccharide fraction (Po-PG), and saponin fraction (Sa-PG) isolated from P. grandiflorum against peroxyl radicals and peroxynitrites. And MTT assay was taken to assess cyto-protective effects of T-PG, Po-PG and Sa-PG in H4IIE cells treated with hydrogen peroxide and tert-butylhydroperoxide. In the TOSC assay, Sa-PG showed strong oxy-radical scavenging capacity compared with T-PG and Po-PG. In cell-based assay, T-PG and Po-PG protected cells from oxidative stress, but Sa-PG did not protect cells because of cytotoxicity of Sa-PG. These results suggest that the saponin components of P. grandiflorum have relatively strong antioxidant capacity and cytotoxicity in rat hepatoma cells.