Abstract： Objective To evaluate the growth inhibition and apoptosis of human monocytic leukemia THP-1 cell line by using 5,8-dimethyl-2-β-hydroxyisovalerylshikonin (SK36) and explore its preliminary mechanism. Methods CCK colorimetric assay and cell counting was used to examine the growth inhibition of shikonin on THP-1 cells. The apoptosis of THP-1 cells was detected by Annexin V/PI double labeling. The activation of Caspase-3 apoptosis pathway was determined by FCM. The apoptosis and the necrosis of THP-1 cells were detected by the laser scanning confocal microscopy. Results When the THP-1 cells were treated with SK36 at 1.02 μg/ml for 24 h and 48 h, the growth inhibition was dose-dependent. The cell apoptotic rate of THP-1 cells treated with 1.02 μg/ml evaluated by FCM with Annexin V/PI double labeling staining were (40.61 ±2.13) % and (67.40±9.15) % at 24 h and 48 h after treatment, respectively, which were significantly higher than that of the control group [(16.97±0.61) %] ([ = 18.444, t = 9.528, P <0.01). SK36 could induce THP-1 cells apoptosis involving the activation of Caspase-3 (F= 323.61, P<0.01). Conclusion SK36 can induce human THP-1 cells to undergo apoptosis, and its primary mechanism was to activate the Caspase-3.