Hepatocellular carcinoma (HCC) is one of the most deadly cancers that still lacks effective treatments. Dysregulation of kinase signaling has frequently been reported to contribute to HCC. In this study, we used bioinformatic approaches to identify kinases that regulate gene expression changes in human HCCs and two murine HCC models. We identified a role for calcium/calmodulindependent protein kinases II gamma isoform (CAMK2γ) in hepatocarcinogenesis. CAMK2γ-/- mice displayed severely enhanced chemical-induced hepatocarcinogenesis compared with wild-type controls. Mechanistically, CAMK2γ deletion potentiates hepatic activation of mechanistic target of rapamycin complex 1 (mTORC1), which results in hyperproliferation of hepatocytes. Inhibition of mTORC1 by rapamycin effectively attenuates the compensatory proliferation of hepatocytes in CAMK2γ-/- livers. We further demonstrated that CAMK2γ suppressed growth factor- or insulin-induced mTORC1 activation by inhibiting IRS1/AKT signaling. Taken together, our results reveal a novel mechanism by which CAMK2γ antagonizes mTORC1 activation during hepatocarcinogenesis.