Objective To study the function of Bak in mitochondrial signaling pathway and interaction between Bax and Bak during apoptosis.Methods Bax/Bak double knock out(Bax-/- and Bak-/-)MEF cells from mouse embryo fibroblasts(MEF) and Hela cells were divided into four groups according the cell different genotypes(wild type,Bax-/-,Bak-/- and double knock out) and treated with different chemical reagents after co-transfection with Bax,Bak,Mito-Red and empty pEGFP vector.Apoptosis,mitochondrial morphology and cytochrome C release were detected with confocal microscope,immunofluoresence and Western blotting techniques.Results There were correlations between the percentage of Hela cell apoptosis and mitochondrial fission(%) as well as cytochrome C(%)(P