This study was conducted to investigate the content of antioxidant and GST activity of the oxyfluorfen-tolerant and -susceptible rice cultivars with barnyardgrass, a typical susceptible weed in accordance by oxyfluorfen treatment. The content of vitamin C was higher in the tolerant rice cultivar than in the susceptible rice cultivar and barnyardgrass. The contents of vitamin E, carotenoid, glutathione(GSH, GSSG, total glutathione) were not different between the tolerant and susceptible plants. In the case of the content of vitamin C due to the treatment of oxyfluorfen, the tolerant rice cultivars, Hawon and Baru decreased less than the susceptible rice cultivars and barnyardgrass. After the treatment of oxyfluorfen the contents of vitamin E and GSH in the tolerant rice cultivars were higher than in the susceptible rice cultivars or barnyardgrass. But in the content of carotenoid was greater in the tolerant rice cultivars than in the susceptible rice cultivars but they didn`t have any difference in comparison with the susceptible barnyardgrass. And there was no difference in the content of GSSG between the tolerant and susceptible plants. When CDNB or oxyfluorfen were used as substrate, the GST activity, was higher in the tolerant rice cultivars than in the susceptible rice cultivars or batnyardgrass. After the treatment of oxyfluorfen the GST activity was not induced in the rice, but was induced in the barnyardgrass. Even after the treatment of acifluorfen, bifenox and oxadiazon the GST activity was not induced in the rice cultivars.