To investigate the effects of the rare earth element cerium (Ce) on the life span and biomarkers of oxidative stress in the fruit fly (Drosophila melanogaster). Fruit flies were fed on media with different dose of ceric sulfate (1, 4, 16, 64, 256, 1024mg/L, corresponding to cerium concentrations of 0.45, 1.65, 6.91, 26.3, 104, and 429microg/g culture medium). Mean life span, maximum life span, and fertility were calculated. There was a significant decrease in mean life span and maximum life span with increasing doses of cerium. At some concentrations, there was a decrease in reproductive output, especially concentrations >6.91microg/g. We also measured superoxide dismutase (SOD) activity, catalase (CAT) activity, and lipid peroxidation product levels (malondialdehyde (MDA) content). Cerium caused a significant increase in MDA content and decrease in SOD and CAT activities at concentrations >6.91microg/g. These results suggest that cerium may result in oxidative toxicity to D. melanogaster.