Aim To investigate the effect of alisol A 24-acetate on the phenotypic modulation of vascular smooth muscle cells（VSMC）as well as the expression of matrix metalloproteinase-9（MMP-9） in ox-LDL-induced rats vascular smooth muscle cells （VSMC）, and their correlation with ERK1/2 pathway. Methods VSMC isolated from the thoracic aorta of rats were induced by ox-LDL（50 mg/L） and intervened by alisol A 24-acetate （10 mg/L）. Immunocytochemistry was performed to detect the expression of SM22α protein.RT-PCR was performed to detect MMP-9 mRNA expression and Western blot was applied to detect the expressions of MMP-9, p-ERK and t-ERK. Results The contractive phenotypic specificity protein SM22α in the VSMC induced by ox-LDL was inhibited, VSMCs changed the phenotype from constriction to synthesis, the expression of phosphorylated ERK （p-ERK） and MMP-9 in ox-LDL group were elevated compared with the control group（P<0.05）. Alisol A 24-acetate.partially inversed the effects of ox-LDL on VSMC （P<0.05）. Conclusion Alisol A 24-acetate inhibited the phenotype transformation of VSMC induced by ox-LDL，and the mechanism maybe has correlation with ERK1/2 pathway.