Objective To investigate the effect of meisoindigo inducing primary K562 cell apoptosis and its influence on the expression of conduction signal STAT5.Methods K562 cell was treated with meisoindigo for 12 h、24 h、48 h respectively.Flow cytometry was used to detect cell apoptosis and cell cycle,and Western blot was employed to examine the alteration of the expression of STAT5.Results ①The rate of K562 cell apoptosis treated with meisoindigo for 12 h、24 h、and 48 h was 12.5 ± 0.69,19.4± 1.07 and 42.5 ± 3.22,showing statistical significance compared with the control group (P＜0.05).②Meisoindigo could block K562 cell at the S stage,the ratio of S stage cell was increased to 70.48±6.34 with the decrease of cells at G0/G1 and G2/M stage.③Gradually reduced expression of STAT5 showed after K562 cells treated with meisoindigo from 12h to 48h.Conclusion Meisoindigo accelerrates the apoptosis of K562 cell and the mechanism may relevant to the decreased expression of STAT5.