Abstract: Hepatocellular carcinoma (HCC) is a serious threat for human health, the incidence of HCC in China accounts for more than 50% worldwide. There is an urgent need to develop novel anticancer agents for the treatment of HCC patients. Here we characterized the inhibitory effect and the molecular mechanism of protopine on HCC cancer cells. The results of a CCK-8 assay indicated that protopine displays anticancer activities on HCC cells. Flow cytometry and JC-1 staining confirmed that treatment with protopine decreased the mitochondrial membrane potential and induced apoptosis in HCC cells. Western blot analysis showed that protopine was able to increase protein expression in the mitochondrial apoptotic pathway; the level of cytochrome C, apoptotic protease activating factor-1 (Apaf-1), Bax, cleaved-poly ADP-ribose polymerase (cleaved-PARP), cleaved-caspase-3, and cleaved-caspase-9 were increased while the expression of Bcl-2 was suppressed significantly. An in vivo study revealed that protopine significantly suppressed the growth of tumors in nude mice bearing HepG2 cells. Administration of protopine intraperitoneally at a concentration of 50 mg·kg^-1 inhibited tumor growth by 72.46%. Animal experiments were carried out according to the Regulation of the Animal Ethics Committee of Southwest Medical University. This study provides preliminary evidence that there is potential to develop protopine as a lead compound for the treatment of HCC.