Abstract: Effect of β-cypermethrin and permethrin on the viability of Drosophila embryo S2 cells, Spodoptera frugiperda Sf-9 cells, human cervical carcinoma HeLa cells, human hepatocellular carcinoma HepG2 cells and human embryonic kidney HEK293 cells was investigated by using MTT method. The results showed that β-cypermethrin and permethrin could inhibit cell viability as well as promote cell proliferation. The inhibitory effects of β-cypermethrin and permethrin with concentration more than 50 μg/mL on the cell viability of S2, Sf-9, HeLa and HepG2 significantly enhanced as the concentration increased and exposure time prolonged, but there was no significant difference between the IC50 values of β-cypermethrin and permethrin. However, 10 or 25 μg/mL β-cypermethrin and permethrin could promote the proliferation of S2 and Sf-9 cells, and 10-200 μg/mL of β-cypermethrin and permethrin could strongly promote the proliferation of HEK293 cells, but this effect was gradually weakened as the exposure time prolonged. Moreover, 10, 25, or 50 μg/mL permethrin could significantly enhance the proliferation of HeLa cells. HepG2 cells were more sensitive to β-cypermethrin and permethrin than HeLa cells. Acridine orange staining showed that 100 μg/mL β-cypermethrin and permethrin could cause HeLa cell deformation, pyknosis and necrosis. The action of β-cypermethrin on cell viability was faster than that of permethrin at the same concentration, and permethrin was more powerful in promoting the proliferation of human cells than β-cypermethrin.