The effect of triptolide on proliferation and apoptosis of human multiple myeloma RPMI-8226 cells in vitro, as well as the roles of nuclear factor-kappa B (NF-κB) and IκBα was investigated. The effect of tritptolide on the growth of RPMI-8226 cells was studied by MTT assay. Apoptosis was detected by Hoechest 33258 staining and Annexin V/PI double staining assay. The expression of NF-κB and IκBα was observed by Western blot and confocal microscopy. The results showed that triptolide inactivated NF-κB apoptotic pathway in human multiple myeloma RPMI-8226 cells. Triptolide at nM range induced proliferation inhibition in a dose- and time-dependent manner and apoptosis in a dose-dependent fashion in RPMI-8226 cells. Besides, we observed the inhibition of NF-κB /p65 in the nuclear fraction was correlated with the increase in the protein expression of IκBα in the cytosol. These results suggested that triptolide might exhibit its strong anti-tumor effects via inactivation of NF-κB/p65 and IκBα.