Apoptosis action is primarily exerted at the level of mitochondira, in which Bcl-2 family of proteins play an important role in its regulation. Bcl-2 family consists of anti-apoptotic and pro-apoptotic members. The anti-apoptotic members usually exist in the outer mitochondrial membrane and inhibit cell death via interaction with pro-apoptotic counterparts BH3 domain. Pro-apoptotic members are commonly localize in the cytoplasm. A series of events occured, such as typical Bax conformational change, BAD and Bik phosphorylation as well as Bid and Bim proteolysis in response to several death stimuli. As a result, these pro-apoptotic proteins directly integrate to the outer mitochondrial membranes. Finally, mitochondrial permeability transition pore is opened, by followed the release of apoptogenic factors from the mitochondrial intermembrane space, including cytochrome c, apoptosis inducing factor(AIF) and Smac, then the activation of downstream caspases and execution of cell death.