The purpose of the present study was to investigate whether the sulfonamide—imidazole (IVb) had radiosensitization effects on H22 tumor. Mice with H22 epatoma were randonized into eight groups:control; radiation alone; radiation+ip 0.58g/kg IVb; radiation+ip 0.29g/kg IVb; radiation+ip 0.14g/kg IVb; ip 0.5g/kg IVb alone; ip 0.29g/kg IVb alone; ip 0.14g/kg IVb alone. IVb was diluted with normal saline and administered to the mice before irradiation. The dose of radiation is 10Gy. Each group was treated mentioned above,[1],. The volume of mice's tumors was measured every two days,[2],. We calculated relative tumor growth rates,[3], tumor inhibition rates and days of tumor growth delay,[4],. At the doses of 0.58g/kg, 0. 29g/kg and 0.14g/kg IVb with ,γ,—ray radiation,the relative growth rates decreased and the tumor inhibition rates, the days of tumor growth delay increased, respectively. Among the three doses, the inhibition effects on tumors was most significant at the dose of 0.29g/kg. There was no effect when IVb was adimin istered alone. The results indicated that IVb has some radiosensitization effects on H22 hepatoma in vivo.