The study was aimed to investigate the effects of bortezomib (BTZ) on the expression of ERK, JNK and P38 in daunorubicin (DNR)-resistant K562 cells (K562/DNR) and to clarify the molecular mechanism of BTZ in reversing the drug-resistance in leukemic cells. The K562/DNR cells and the cellular toxicity of BTZ was determined by MTT, then 4 µg/L of BTZ was chosen to do the experiment. The expression of ERK, JNK, p38 and P-gp of K562/DNR cells treated with DNR only or DNR combined with BTZ for 12, 24 and 36 hours was detected by Western blot. The apoptosis rate in each group was assayed by flow cytometry. The results showed that as compared with DNR group, the expression of P-ERK, P-P38 and P-gp was significantly suppressed (p < 0.05) and the expression of P-JNK was significantly enhanced (p < 0.05) in the cells treated with DNR combined with BTZ. There was no change in the expression of total ERK, P38 and JNK. The effect increased with the prolonging of time. Meanwhile, the apoptosis rate in cells treated with DNR combined with BTZ increased compared with DNR only. It is concluded that the BTZ can reverse the drug resistance in K562/DNR cells by MAPK signaling pathway and increase the apoptosis of leukemic cells. The effect shows the characteristics of time-dependent manner.