Objective: To determine whether neferine (Nef) enhances the sensitivity of human myeloid leukemia HL-60 cells to arsenic trioxide (ATO). Methods: Apoptosis was detected by DNA electrophoresis. Giemsa staining was used to observe the apoptotic cells under microscope. The apoptotic rates of cells were analyzed using flow cytometry. The inhibitory rates of cell growth were assayed by MTT, and the expression of P-gp was determined by flow cytometry. Results: Low doses of ATO (1.0 (mol/L) only partially inhibitory percentage of cell growth at 72 h was (9.92(3.03) % (P＞0.05, vs control). The combination of 1.0 (mol/L ATO with 2.0 (mol/L Nef inhibited (45.27(4.93) % of cell growth, and induced apoptosis in leukemic cells more significantly than wither ATO or Nef on their own (P＜0.01). Moreover, ATO-induced expression of P-gp in leukemic cells was inhibited significantly by Nef. Conclusion: These results indicate that Nef significantly increases sensitivity of leukemic cells to ATO, which might be associated with inhibitory expression of P-gp gene. Combined use of the two agents could be a novel and attractive strategy in leukemia treatment.