Abstract: Objective : To study the reversal effect of multidrug resistance by P -elemene and its possible mechanism in K562/ADM cell lines. Methods : The reversal of drug resistance was examined by using MTT assay. The expression of BCl-2 protein and P-gp were observed by immunohistochemistry . The apoptosis percentage of K562/ADM cells and the expression of P-gp and BCl-2 protein were detected by flow cytometry. Results : Non-cytotoxic dose of P-elemene (4.0ug/ml) could obviously decrease the IC₅₀ value of K562/ADM cells on adriamycin (ADM),with a reversal of 2.18 fold as compared to that of K562 cells its parental cell lines.lt could remarkably enhance the effect of inducing apoptosis of K562/ADM cells. The apoptosis percentage was increased from (1.88±0.11)W to (3.93±0.06)W. It could obviously decrease expression of the BCl-2 protein and P-gp in K562/ADM cells. Expression of the BCl-2 protein was decreased from (94.8±1.9)W to (66.7±0.9)W. Expression of the P-gp was decreased from (98.7±2.1)W to (76.8±1.4)W. Conclusions : β-elemene could partly reverse ADM resistance of K562/ADM cell line, which may be related to the decreased expression of BCl-2 and p-gp.