Abstract： Objective To investigate the effect of bortezomib on the proliferation and apoptosis in leukemia cell line NB_4-R2 in vitro and provide some new evidences for the treatment of acute promyelocytic leukemia APL with ATRA-resistant using bortezomib. Methods NB_4-R2 cells were incubated with bortezomib at different does for 48 h. The proliferation capacity was measured by MTT assay, the morphology of cell apoptosis observed with Hoechst33342 staining by fluorescence microscopy and the percentage of apoptosis calculated by flow cytometry. The expression of apoptosis protein of cleaved (poly ADP-ribose polymerase, PARP) and Caspase-3 were determined by Western blotting. Results The proliferation of NB_4-R2 cells were obviously inhibited by bortezomib in vivo and the role of inhibition was a does-dependant manner within the scope of the bortezomib concentration from 1-5 μg /L.The incidence of inhibition was up to 74.9 % at the bortezomib concentration of 5 μg/L. Within this scope of the bortezomib concentration mentioned above, the role of inhibition of proliferation of NB_4-R2 cells mainly showed an increase of the late apoptosis, and the percentage of apoptosis was up to 78.9 %. In the meaning time, the expressions of the apoptotic protein of cleaved PARP and Caspase-3 were up-regulated in NB_4-R2 cells after treated with bortezomib by Western blotting assay. Conclusion Bortezomib can inhibit the proliferation of NB_4-R2 cells in vivo by inducing cell apoptosis.