Abstract: Objective : To investigate the effects and mechanism of Oxymatrine at non-cytotoxic concentrations in re-versing multidrug resistance (MDR) in the K562/A02 leukemia cell line. Methods : MTT colorimetry was usedto detect the cytotoxic effect of oxymatrine and the sensitivity to Adriamycin of the K562/A02 cell line. Flow cy-tometry was employed to measure glycoprotein-170 (P170) on the membranes of cells treated with Oxyma-trine at the non-cytotoxic concentration. The concentration of Daunorubicin in the cells was detected by flowcytometry. The experimental data were analyzed with SPSS13.0 software. Results : Oxymatrine had a definitecytotoxic effect on K562/A02 cells. The non-cytotoxic dose of Oxymatrine was 50 μg/mL, and the low-cytotox-ic dose of Oxymatrine was 135 μg/mL. The non-cytotoxic dose of Oxymatrine significantly decreased thehalf-maximal inhibitory concentration (IC50) value of Adriamycin in the K562/A02 cell line. The IC50 was sig-nificantly reduced from 34.9±0.21 μg/mL to 13.3±0.21 μg/mL. Oxymatrine at the non-cytotoxic concentrationcould partly reverse MDR in K562/A02 cells by 2.62-fold and could decrease the expression of P170 from90.22% to 44.24%. The daunorubicin exosmosis test showed that the intracellular concentration of chemother-apeutics was increased. Conclusion : In K562/A02 cells oxymatrine can partly reverse MDR, decrease the ex-pression of P170, and inhibit the pumping of chemotherapeutics out of the cel1, a feature quite helpful forkilling multidrug resistant leukemia cells.