Recent studies indicate that beta-elemene, a compound isolated from the Chinese herbal medicine Curcuma wenyujin, is capable of reversing tumor MDR, although the mechanism remains elusive. In this study, beta-Elemene treatment markedly increased the intracellular accumulation of doxorubicin (DOX) and rhodamine 123 in both K562/DNR and SGC7901/ADR cells and significantly inhibited the expression of P-gp. Treatment of SGC7901/ADR cells with beta-elemene led to downregulation of Akt phosphorylation and significant upregulation of the E3 ubiquitin ligases, c-Cbl and Cbl-b. Importantly, beta-elemene significantly enhanced the anti-tumor activity of DOX in nude mice bearing SGC7901/ADR xenografts. Taken together, our results suggest that beta-elemene may target P-gp-overexpressing leukemia and gastric cancer cells to enhance the efficacy of DOX treatment.