In order to investigate the effects of sodium selenite on the activity of glutathione peroxidase and the life-span of drosophila melanogaster, newly enclosed flies were divided randomly into 4 groups and fed with mediums containing different concentrations of sodium selenite. The activity of GSH-Px was determined by 5,5'-dithionbis (2-nitrobenzoic acid) (DTNB) photometric method. The life-span of drosophila was calculated after survival test. The results showed that the activity of GSH-Px in the female and male flies were increased by the increase of sodium selenite in the medium (P < 0.05). The average life-span and the average maximum life-span of flies in selenium groups were increased significantly as compared with control group (P < 0.05). The response of GSH-Px activity and life-span of male flies to selenium intake was better than that of females.