Herein, we find a novel biological function of miR-122 in attenuating de novo BA production in liver via targeting BA synthesis gene HSD3B7, and the loss of miR-122 in hepatocytes in paracancerous tissues leads to enhanced BA biosynthesis, which in turn facilitates cancer cell proliferation and HCC tumor growth. The gene discussed is HSD3B7; the disease is hepatocellular carcinoma.