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 H2O2 in the presence or absence of different concentrations(10-10mol/L-10-8mol/L) of 17β-estradiol (E2). The expressions or activities of senescence associated marker DcR2, senescence-associated beta-galactosidase (SA-β-Gal), oncogene Ras and p21WAF1 were detected by flow cytometry, cytochemical staining, pull-down assay or Western blotting analysis. Results Flow cytometry analysis showed that in the physiological concentrations, E2 significantly inhibited the H2O2-promoted high-level expression of DcR2 of VSMCs in a dose-dependent manner, with a highest inhibitive rate at 14.48%±0.6%(E2=10-8 mol/L;P<0.05, n =3);this inhibitive effect could be blocked by a E2 receptors inhibitor ICI 182,780. Cytochemistry staining showed that the rate of SA-β-Gal positive VSMCs induced by H2O2 decreased in presence of 10-8mol/L E2 (20.5%±1.4% vs 9.6%±0.9%;P<0.05, n =9). Pull-down assay and Western blotting analysis revealed that administration of 10-8mol/L E2 obviously reduced the H2O2-induced activity of Ras (0.60±0.06 vs 0.26±0.04;P<0.05, n =3) and expression of p21WAF1 (0.46±0.04 vs 0.33±0.02;P<0.05, n =3). Conclusion E2 exerts, an inhibitive effects on stress-induced senescence of VSMCs by suppressing the activity of Ras and expression of p21WAF1. This finding suggests a novel mechanism for the hormone's anti-atheroschlerotic effects.