Frizzled (Fz), a receptor of Wnt ligands, plays key roles in liver carcinogenesis. Its expression was analyzed as part of a search for a target of molecular therapy for hepatocellular carcinoma (HCC) and hepatoblastoma (HB). Fz genes were analyzed by RT-PCR in HCC cell lines HLE, HLF, PLC/PRF/5, Huh-7 and Hep3B, HB cell lines Huh-6 and HepG2, HeLa cells, human normal fetal and adult liver. We transfected PLC/PRF/5, HLE, Huh-6, and HeLa cells with Fz9-small interfering RNA (Fz9-siRNA). Five days after transfection, cell proliferation was analyzed by MTS assay and cell motility by wound assay with H&E staining. Subsequently, the expressions of cyclin D1 and caspase-3 were analyzed by Western blot analysis. Fz9-siRNA decreased the expression of Fz9 gene in all cell lines. MTS assay showed that Fz9-siRNA significantly suppressed cell proliferation and cell motility in all cell lines. The expression of cyclin D1 was also suppressed by Western blotting. Cleaved caspase-3 did not appear and apoptosis was not observed in any of the cell lines tested. We demonstrated that Fz9 plays an essential role in carcinogenesis of HB and HCC, concluding that Fz9-siRNA could represent a useful therapeutic target for HB and HCC.