Abstract: AIM: To examine the pro-angiogenesis effect of 17β-estradiol (E2) on rat cardiac microvascular endothelial cells (CMECs) in vitro. METHODS: Rat CMECs were primarily cultured in vitro and the expression of estrogen receptor (ER) protein was observed by immunofluorescence. Cell proliferation was determined with MTT method after cells were treated with increasing concentrations of 17β-estradiol (E2). Cell migration ability was evaluated by wound scraping. CMEC invasion was measured using transwell chamber and the differentiated ability of CMECs was examined by tube formation assay. VEGF secretion was detected by enzyme-linked immunosorbent assay. RESULTS: ER protein was expressed in CMECs. 17β-E2 obviously promoted cell proliferation and the highest proliferation rate was determined at a concentration of 0.01 μmol/L. At the concentration of 0.01 μmol/L, 17β-E2 significantly enhanced the migration and tube-like formation of CMECs (P<0.01 vs. control group). The secretion of VEGF significantly increased at the concentration of 0.01 μmol/L (P<0.01 vs. control group). The pro-angiogenesis effect of 17β-estradiol (E2) was blocked by estrogen antagonist tamoxifen. CONCLUSION: In vitro, estradiol enhances CMEC biological activities and has some pro-angiogenesis effects.