The purpose of the study was to investigate the role of flavonoids from Emilia sonchifolia (ES) on the progression of selenite-induced cataract. The antioxidant property of the flavonoids isolated from ES was assessed by measuring its capacity to inhibit superoxide production and serum oxidation in vitro in comparison with quercetin. Based on these experiments, an in vivo study was conducted to evaluate the modulatory effects of the flavonoids against selenite cataract. Cataract was induced by a single subcutaneous injection of sodium selenite (4 mg/kg body weight). The treatment group received flavonoids from ES (1 mg/kg) and this was compared with the quercetin treated group. Lens opacification was monitored by a slit lamp microscope and classified into six stages. Activity of the antioxidant enzymes - superoxide dismutase and catalase - and the level of lipid peroxidation products thiobarbituric acid reacting substances and reduced glutathione were studied. Slit lamp examination showed that the flavonoid fraction from ES could modulate the progression of cataract. Activities of superoxide dismutase, catalase and reduced glutathione were found to be increased in the ES treated groups, while thiobarbituric acid reacting substances were decreased compared with the selenite-induced group. The results suggest that flavonoids from ES can modulate lens opacification and oxidative stress in selenite-induced cataract.