AIM: To investigate the effect of 17?-estradiol on insulin action in cultured C2C12 mytoblasts. METHODS: C2C12 mytoblasts were cultured in 35 mm wells of six-well culture plate in an atmosphere of 5% CO 2 at 37℃ in DMEM supplemented with 10% FBS and penicillin/streptomycin(1?10 5 U/L) to reach 80% confluence. Insulin-resistance C2C12 mytoblasts were obtained by incubating the cells for 24 hours in the presence of a high concentration (5?10 -7 mol/L) of insulin. After treatmented with 17?-estradiol (1 nmol/L and 10 nmol/L, respectively) for 24 hours, C2C12 mytoblasts were performed to measure insulin-stimulated 2-DG uptake and GS, PFK, PK activities. RESULTS: 17?-estradiol enhanced the capacity of insulin-stimulited 2-DG uptake, increased the GS, PFK and PK activities and prevented insulin-induced resistance in cultured C2C12 mytoblasts. CONCLUSION: 17?-estradiol potentiates insulin action and preventes insulin-induced resistance in cultured C2C12 mytoblasts.