Abstract: Established human breast cancer MCF7 cell line stably expressed GFP-Bax, which was used to investigate Bax translocation from cytosol into mitochondria induced by TNFα. Bax translocation from cytosol into mitochondria and DNA fragmentation were investigated under fluorescence microscope. The viability of cells treated with TNFα was measured by MTT method. Immunofluoresence method was used to investigate Bax translocation to mitochondria and Cyt-c release from mitochondria. The Dose-effect and time-course relationship were also observed and calculated by the percentage of GFP-Bax punctate cells. The TMRE assay was used to investigate the function of mitochondria. The results showed that Bax translocation from cytosol into mitochondria was associated with apoptosis induced by TNFα in hGFP-Bax-tagged MCF7 stable cell line.