Cyanidin 3-glucoside (C3G) isolated from black rice was investigated for hepatoprotective effects in HepG2 cells under oxidative stress. When an increase in the production of reactive oxygen species (ROS) was induced by gramoxone, cell viability was drastically decreased by 42%. However, in the presence of C3G, no hepatocytic damage was observed in HepG2 cells treated with gramoxone. C3G was found to manifest a stronger scavenging effect (91%) on superoxide anion radical ($O_2;^{.-}$) than any of the other natural and synthetic antioxidants. Results suggest that C3G from black rice possesses hepatoprotective effects in vitro, which may be, at least in part, due to $O_2;^{.-}$ scavenging.