The roles and characteristics of DNA polymerase ,β, of hepatoma cells in participating in DNA repair synthesis induced by ,60,Co γ-rays irradiation were studied. Transplanted SMMC-LTNM hepatoma in mice was used as a tumor cells model. NEM and d,2,TTP were used as selective inhibitors to DNA polymerase α and ,β, respectively. It was showed that the polymerase ,β, could take part in repair synthesis of DNA damaged by γ-rays. The increment of ,3,H-TTP incorporation into DNA of SMMC-LTNM hepatoma cells nuclei was higher than that of normal hepatocyte nuclei (P,<,0.01). The DNA repair synthesis induced by DNA polymerase ,β, reacted more fast in hepatoma cells nuclei than in hepatocytes nuclei too. These results indicated that the DNA repair synthesis of polymerase ,β, in some tumor cells might be stronger than normal cells.