In order to study the influence of trichosanthin (TCS) on apoptosis and growth inhibition of human NB4 cells in vitro, the expression of annexin V and the change of DeltaPsim of NB4 cells induced by TCS was analyzed by FACS, and MTT assay was adopted to measure the growth inhibition ratio of NB4 cells treated with TCS. Apoptosis was assayed by agarose gel electrophoresis. The results showed the higher concentration of TCS and the longer the acting time, the stronger growth inhibition of NB4 cells. The expression of annexin V was positive, and the positive ratio was greatly enhanced with prolongation of acting time. DeltaPsim reduced gradually while the apoptosis cells increasing. DNA agarose gel electrophoresis showed a gradient, which confirmed that TCS could induce NB4 cells apoptosis. In conclusion, taken together, data show that TCS can inhibit NB4 growth in vitro, and induce apoptosis. Experiment provides an important evidence for application of TCS in clinical treatment of acute promyelocytic leukemia.