Abstract: Objective To investigate the inhibitory effects of Tanreqing（phlegm and heat clearing） injection on proliferation of chronic myelogenous leukemia K562 cell line. Methods Tanreqing injection was diluted to 9 groups at the concentration of 1:2,1:4,1:8,1:16,1:32,1:64,1:128,1:256 and 1:512,respectively.Proliferating chronic myelogenous leukemia K562 cells were treated with Tanreqing injection at different dilution concentrations and their growth was observed at different time points under a microscope.CCK-8 assay was employed to detect the ability of the cells to proliferate and growth curves were plotted for calculating the inhibition ratio and 50% inhibiting concentration（IC₅₀） of Tanreqing. Results Tanreqing injection could significantly inhibit the proliferation of K562 cells.The proliferating time of the cells was 24h.The cytotoxicity of Tanreqing injection was greater in 1:2,1:4 and 1:8 concentration groups with almost all the cells died.Tanreqing injection inhibited the proliferation of K562 cells in a time-and dose-dependent manner and its IC₅₀ was approximately 1:55 dilution concentration. Conclusion Tanreqing injection can inhibit the proliferation of K562 cells,thus laying a foundation for its use in treatment of hematological malignancies complicated by infection.