Previous studies have demonstrated that polypeptides extracted from scorpion venom (PESV) inhibited cell proliferation in several tumors, however, the effect on dysfunctional and exhausted natural killer cells which contribute to tumor escape from immune surveillance remain to be elucidated. In this study, we determined the effect of PESV on NK infiltration into H22 cells orthotopic transplantation tumors and on the expression of MHC class I chain-related proteins A (MICA) in HepG2 cells. We found that tumor growth in mice was significantly inhibited by PESV and the survival time of tumor-bearing mice treated with PESV was significantly prolonged. Moreover, levels of tumor-infiltrating NK cells, NKG2D protein, perforin and granzyme B mRNA were significantly increased in the group treated with PESV compared with the tumor-bearing control group. In addition, In addition, up-regulation of MICA by PESV enhances the susceptibility of HepG2 cells to NK lysis in vitro. These results indicate that the inhibitory effects of PESV on hepatic carcinoma are likely mediated by up-regulation of NK cell activity via the MICA-NKG2D pathway.