ObjectiveTo investigate the anti-proliferation effect of oridonin on leukemic HL-60 cells and its mechanism. Methods HL-60 cells invitroin culture medium were given different concentrations of oridonin. The inhibitory rate of cells were measured by microculture tetrazolium （MTT） assay

cell apoptotic rate was detected by flow cytometry （FCM）

morphology of cell apoptosis was observed by hoechst 33258 fluorescence staining

and the activity of telomerase was det-ected using telomere repeat amplification protocol （TRAP） PCR-ELISA before and after apoptosis occurred. Results Oridonin could decrease telomerase activity

inhibit growth of HL-60 cells

and cause apoptosis significantly. The suppression was both in time- and dose-dependent manner. Marked morphological changes of cell apoptosis including condensation of chromatin and nuclear fragmentation were observed clearly by hoechst 33258 fluorescence staining especi-ally after cells were treated 48-60 hours by oridonin. Conclusions Oridonin has apparent anti-proliferation and apoptotic effects on HL-60 cells invitro

decreasing telomerase activity of HL-60 cells may be one of its most important mechanisms. These results will provide strong laboratory evidence of oridonin for clinical treatment of acute leukemia.