Objective To explore the effects of estrogen on stressinduced senescence of vascular smooth muscle cells (VSMCs) and the underlying mechanisms. Methods The VSMCs of passage 23 cultured from female SD rats were induced into senescence by exposing to 150μmol/L HSUB>2/SUB>OSUB>2/SUB> in the presence or absence of different concentrations(10SUP>-10/SUP>mol/L10SUP>-8/SUP>mol/L) of 17β-estradiol (ESUB>2/SUB>). The expressions or activities of senescence associated marker DcR2, senescence-ssociated beta-galactosidase (SA-β-Gal), oncogene Ras and p21SUP>WAF1/SUP> were detected by flow cytometry, cytochemical staining, pulldown assay or Western blotting analysis. Results Flow cytometry analysis showed that in the physiological concentrations, ESUB>2/SUB> significantly inhibited the HSUB>2/SUB> OSUB>2/SUB>promoted highlevel expression of DcR2 of VSMCs in a dosedependent manner, with a highest inhibitive rate at 14.48%±0.6%（ESUB>2/SUB>=10SUP>8/SUP>mol/L;EM>P/EM><0.05, EM>n/EM>=3）; this inhibitive effect could be blocked by a ESUB>2/SUB> receptors inhibitor ICI 182,780. Cytochemistry staining showed that the rate of SA-β-Gal positive VSMCs induced by HSUB>2/SUB>OSUB>2/SUB> decreased in presence of 10SUP>-8/SUP>mol/L ESUB>2/SUB> (20.5%±1.4% vs 9.6%±0.9%;EM>P/EM><0.05, EM>n/EM>=9). Pulldown assay and Western blotting analysis revealed that administration of 10SUP>-8/SUP>mol/L ESUB>2/SUB> obviously reduced the HSUB>2/SUB>OSUB>2/SUB>induced