OBJECTIVE：To investigate the effects and its mechanism of pseudostrychnine on the apoptosis of human colon can - cer HT- 29 cells. METHODS ：Human colon cancer HT- 29 cells were randomly divided into blank group ，pseudostrychnine low-dose，medium-dose and high-dose groups （125，250，500 μmol/L）. They were cultured with culture medium without medicine or relevant concentration of pseudostrychnine for 48 h. The cell apoptosis and mitochondrial transmembrane potential were detected by flow cytometry. Western blotting assay was employed to detect the protein expression of P 53，Caspase-3，Caspase-9，DNA re - pair enzyme from rabbit （c-PARP）and Bcl- 2. RESULTS ：Compared with blank group ，apoptotic rate of cells was increased signifi - cantly in pseudostrychnine low-dose ，medium-dose and high-dose groups ，while mitochondrial transmembrane potential was de - creased significantly （P＜0.01），in concentration-dependent manner. The protein expression levels of P 53，Caspase-3，Caspase-9 and c-PARP were increased in pseudostrychnine medium-dose and high-dose groups ，compared with blank group ；while those of Bcl-2 were decreased significantly in pseudostrychnine low-dose ，medium-dose and high-dose groups （P＜0.05 or P＜0.01）. CON - CLUSIONS：Pseudostrychnine may change mitochondrial membrane potential by up-regulating the protein expression of P 53 and down-regulating the protein expression of Bcl- 2，and activate the expression of Caspase- 3，c-PARP and Caspase- 9，so as to acti - vate endogenous mitochondrial pathway and promote the apoptosis of HT- 29 cells.