In the present study, we investigated the effects and action mechanisms of a purified polysaccharide (APWP) from Andrographis paniculata, on human hepatocellular carcinoma (HCC) HepG2 cells. The results showed that APWP was able to suppress the proliferation of HepG2 cells via inducing apoptosis. Western blot analysis revealed that dose-dependent increase in proapoptotic Bax protein and no change in antiapoptotic Bcl-2 protein in APWP-treated cells. Furthermore, exposure of tumor cells to APWP resulted in a loss of mitochondrial membrane potential (MMP) and the release of cytochrome c from the mitochondria to the cytosol. Besides, caspase-9 and caspase-3 were activated while caspase-8 was not affected in HepG2 cells followed by APWP treatment. All these results point clearly to the involvement of mitochondria-mediated signaling pathway in APWP-induced apoptosis and strongly suggest that APWP seems to be safe and effective in the prevention and treatment of HCC.