Abstract： Objective To investigate the apoptosis inducing effects of oridonin on leukemic THP-1 cells and its mechanisms of action. Methods THP-1 cells in culture medium in vitro were given different concentrations of oridonin (16～56 μmol/L) for 24, 48 and 72 h. The inhibitory rate of the cells were measured by MTT assay, apoptotic morphology was observed by Hoechst 33258 staining, and Annexin V/PI staining was used to detect cell apoptosis by flow cytometry (FCM). Caspase-3 and poly (ADP-ribose) polymerase (PARP) expression were detected by Western blotting. Results Oridonin (over 32 μmol/L) could inhibit the growth of THP-1 cells and cause apoptosis remarkably, the suppression was both in time-and dose-dependentmanner. Marked morphological changes of cell apoptosis such as condensation of chromatin was clearly observed by Hoechst 33258 staining, and Annexin V/PI staining showed that apoptotic cells gradually increased after the cells treated with oridinon. Western blotting showed cleavage of the caspase-3 zymogen protein (32×103), with the appearance of its 20×103 subunit, and a cleaved 89×103 fragment of 116×103 PARP was also found. Conclusion Oridonin can inhibit cell growth and induce apoptosis in THP-1 cells via activation of caspase-3. The results indicated that oridonin might be an important potential anti-leukemia reagent.