Abstract: Objective: To investigate the mechanism of isomycin derivant on anti-proliferation and inducing apoptosis of human breast carcinoma MCF-7 cell line in vitro. Methods: MCF-7 cells were cultured in vitro; We investigated the expression of Fas、Caspase-3、Caspase-8、NF-kB by immunohistochemitry and studied the possible mechanism of the apoptosis. Results: Immunocytochemistry showed that Isomycin derivant up-regulated the expression of Fas、Caspase-8、Caspase-3，and they were significantly different from control groups; Isomycin derivant also inhibited signal transduction pathway of NF-kB. Conclusions: Isomycin derivant induced apopsis via extrinsic or death receptor-mediated pathway; Inhibition of the signal transduction pathway of NF-kB may be the mechanism of inducing apoptosis.

Key words: isomycin, breast cancer, cell apoptosis.