Apoptosis or programmed cell death is a normal condition for development and live multicellular organism. Apoptosis is a morphological phenomenon that play important role in physiological processes during fetal development and in adult. Mitochondria play an important role in apoptosis. Mitochondria can do apoptosis directly. Mitochondria has 2 family of protein Bcl-2. Bcl-2 and Bcl-XL are anti apoptosis while Bad and Bax are pro apoptosis. There are 3 different mechanism apoptosis. One generated by signals arising within the cell another triggered by death activators binding to receptors at the cell surface and a third may be triggered by dangerous agent that different from two ways before. Apoptosis also need caspase as cell death executor. Study of apoptosis still done especially in case of disease. Some disease have known related with disturbing of apoptosis mechanism for example cancer and auto immun. This article reviews about molecular mechanism of apoptosis for understanding disease and future therapy.