Abstract: Objective To study the effects of different quantum dots(QDs)(CdSe particles of 2.2 nm and CdTe particles of 2.0 and 3.5 nm in diameter)on proliferation activity,oxidative damage,and apoptosis of L929 cells. Methods Methyl thiazolyl tetrazolium(MTT)assay was applied to test the proliferation activities of L929 cells.Twenty-four hours after the treatment,malondialdehyde(MDA),superoxide dismutase(SOD),glutathione-peroxidase(GSH-Px),and hydroxy radical(·OH)in the cells were determined.The apoptosis was detected with flow cytometry. Results The 50%inhibitory concentrations(IC₅₀)was 27.14μg/mL for 2.2 nm CdSe,28.28μg/mL for 2.0 nm CdTe,and 79.30μg/mL for 3.5nm CdTe,respectively.There were statistically significant differences in·OH and GSH-Px contents between two groups with different size QDs exposure at the dose of 14μg/mL(P<0.05).The apoptosis of each group at the dose of 14μg/mL had significant difference compared with that of the control group and there also was a significant difference between the groups with QDs exposure of different size of the same dose. Conclusion QDs can inhibit the proliferation and induce oxidative damage and apoptosis of L929 cells and the size of QDs is an important influential factor of cytotoxicity.