An outbreak of urinary stones associated with consumption of melamine-tainted milk products occurred in 2008 in China, leading to serious illness of many infants and even death. However, the toxicity of melamine in kidney epithelial cells remains unclear. We have explored the effects of melamine and trolox on renal NRK-52e (normal rat kidney 52e) cells. The IC50 of melamine was measured by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide] assay. Total SOD (superoxide dismutase) was determined by NBT (Nitro Blue Tetrazolium) staining method. GSH-Px (glutathione peroxidase) activity was detected by UV colorimetric assay, and MDA (malondialdehyde) content was determined by thiobarbituric acid assay. Apoptosis induced by melamine was determined by flow cytometry. The IC50 increased when NRK-52e cells were treated with both melamine and trolox compared with melamine only. SOD and GSH-Px activities were decreased, but MDA content was increased by melamine in a dose-dependent manner. Trolox significantly enhanced SOD and GSH-Px activity in melamine-treated NRK-52e cells, but it decreased their MDA content. LDH (lactate dehydrogenase) activity and the level of ROS (reactive oxygen species) of the NRK-52e cells were enhanced by melamine compared with the control. Furthermore, the apoptosis rate increased in NRK-52e cells treated with melamine, whereas trolox was protective. These results show that melamine has an obvious adverse effect on proliferation of NRK-52e cells, causing oxidative damage and apoptosis, thus providing a novel insight into renal cytotoxicology of melamine. Trolox ameliorates the effect on melamine toxicity.