OBJECTIVE To investigate the effect of parthenolide (PTL) on human multiple myeloma (MM) cells in vitro and its mechanism. METHODS Human MM cells of the line PRMI8266 were cultured and treated with PTL of the concentrations of 1, 2.5, 5, 7.5, and 10 micromol/L for 24, 48, or 72 hours. MM cells treated with DMSO were used as control group. The optical density was measured so as to draw a growth curve. The cell viability was detected by MTT and trypan-blue exclusion. The apoptosis was detected by flow cytometry. AO/EB staining and Wright-Giemsa staining were used to observe the morphological changes of the cells by fluorescence microscope and light microscope respectively. The caspase-3 activity was evaluated by BD ApoAlert Caspase Colorimetric Assay Kit. RESULTS PTL significantly inhibited the proliferation and viability of the MM cells time and dose-dependently (all P < 0.01), and significantly induced the cell apoptosis after 48 h in a dose-dependent manner (P < 0.01). The early cell apoptosis rates for PTL of the concentrations of 2, 5 and 10 micromol/L were 17.1% +/- 2.6%, 33.6% +/- 3.8%, and 40.9% +/- 3.1% respectively, all significantly higher than that of the control group (5.6% +/- 1.2%, all P < 0.01). The MM cells treated with PTL of the concentration of 5 micromol/L for 48 h showed typical cell apoptotic features. The caspase-3 activity of the MM cells was enhanced significantly by PTL in a time and dose-dependent manner (all P < 0.01). CONCLUSIONS This first report of anti-proliferation and apoptosis induction effects of PTL on MM cells shows that able to significantly inhibit the proliferation and induce the apoptosis of MM cells and enhance the caspase-3 activity, PTL may be a potentially useful drug for treatment of MM.