OBJECTIVE To investigate the inhibitory effect of natural compound XCQ-9 of Cynanchum paniculatum on the proliferation and apoptosis of Jurkat cell line of human T-cell acute lymphoblastic leukemia and its possible mechanism. METHODS Jurkat cell was used as the leukemia cell model， and MTT assay was adopted to detect the inhibitory effects of 0 （blank control）， 2.5， 5， 10， 20 and 40 μmol/L XCQ-9 on the proliferation of Jurkat cell after treated for 24， 48， 72 h. After treated with 0 （blank control）， 2.5， 5， 10 μmol/L XCQ-9 for 24 h and 48 h， the cell cycle and apoptosis were analyzed by flow cytometry. The expressions of Caspase-9， Cleaved Caspase-9， Caspase-3， Cleaved Caspase-3， poly ADP-ribose poly-merase （PARP）， Cleaved-PARP， cyclin-dependent kinase 1 （CDK1） and Cyclin B1 were detected by Western blot after treated for 24 h. RESULTS Compared with blank control group， XCQ-9 at different concentrations could significantly decrease the survival rate of Jurkat cells （P＜0.01）， and showed a dose and time-dependent manner. After 48 h treatment of 5， 10 μmol/L XCQ-9， Jurkat cell apoptosis was induced significantly （P＜0.05 or P＜0.01）， and the cell was arrested in G2 phase （P＜0.01）. After 24 h treatment of 10 μmol/L XCQ-9， the protein expressions of CDK1 and Caspase-9 were remarkably down-regulated （P＜0.01）， while the protein expressions of Cyclin B1， Cleaved Caspase-9， Cleaved Caspase-3 and Cleaved PARP were significantly up-regulated （P＜0.05 or P＜0.01）. CONCLUSIONS XCQ-9 plays anti-tumor effect through inducing G2 phase arrest to inhibit proliferation and 5008） activating Caspase pathway to increase apoptosis.