Objective To study the cytotoxic effect of the CdSe/ZnS quantum dots of different diameters on human malignant melanoma cell line A375, A375.s2 and normal human epidermal cell line HaCaT using cell counting kit-8（CCK-8）, so as to study the influence of CdSe/ZnS quantum dots on growth of melanoma cells. Methods Log phase A375,A375.s2 and HaCaT cells were plated into 96-well plates. After a 24 h incubation, the prepared QDs-605 and QDs-545 solutions of different concentrations (162, 81, 54, 40.5, 27, 10.125, 4.05, 2.025, and 1.012 5 nmol/L) were added into the wells. After another 24 h incubation, CCK-8 was added into the well (10 μl/well).Then the cytotoxicities of CdSe/ZnS quantum dots on the proliferation of A375, A375.s2 and HaCaT cells were determined by MTT assay. Results We found that with the increase of QDs-605 and QDs-545 concentrations, the survival rates of A375, A375.s2 cells were decreased. A day after A375, A375.s2 cells were treated with different concentrations of QDs-605 and QDs-545, the cell survival rate was significantly lower than that of the control group(P<0.05,P<0.01); however, different concentrations of QDs-605 and QDs-545 did not inhibit the proliferation of HaCaT cells.Conclusion CdSe/Zns quantum dots have inhibitory effect on the growth of human malignant melanoma cell line A375, A375.s2, and have no noticeable effect on normal human epidermal cell line HaCaT.