Objective To investigate the effect of tamoxifen (TAM) on the invasiveness of breast cancer SK-BR-3 cells and its mechanism.Methods The SK-BR-3 breast cancer cells in logarithmic growth period were cultured for 24 h by theserum-free RPMI 1640 culture medium,and then were divided into control group (serumfree RPMI 1640 medium) and TAM group(serum-freeRPMI 16400.5,2.5,12.5 mol·L-1TAM).Western blot was used to detect matrix metalloproteinase-9 (MMP-9),matrix metalloproteinase-2 (MMP-2),and vascular endothelial growth factor (VEGF) in groups.Scratch and transwelhests were used to detect the invasiveness of SK-BR-3 cells.Results The results of scratch test and Transwell experiment showed that the relative invasive ability of SKM-BR-3 cells in TAM (0.5,2.5,12.5 mol/L) group was significantly higher than that in the control group,and the difference was statistically significant (P＜0.05).The invasive ability of SK-BR-3 cells increased with the increase of TAM con centration.The results of Western blot showed that the expression levels of VEGF,MMP-9 and MMP-2 in SK-BR-3 cells of TAM group were average.It was significantly higher than the control group,and the expression levels of VEGF,MMP-9 and MMP-2 in SK-BR-3 cells increased gradually with the increase of TAM concentration.Conclusion Tamoxifen may play the role of estrogens and promote the invasiveness of SK-BR-3 breast cancer cells,via increasing the expression levels of VEGF,MMP-9 and MMP-2.