In order to investigate radiation effects on the liver, functional changes of liver were analyzed after irradiation. Doses of 10 Gy, 15 Gy and 20 Gy were exposed partially to the liver of male rats(Sprague-Dawley) with X-ray(4MV linear accelerator) at room temperature. On 1, 2, 4 and 8 weeks after irradiation, liver tissues and sera of the animals were compared with those of unirradiated animal by liver function tests. Enzyme activities in sera such as alanine aminotransferase, aspartate aminotransferase, malondialdehyde. The content of malondialdehyde in the activities of many enzymes including alanine aminotransferase, aspartate aminotransferase in sera were increased slightly with increasing exposure dose in all experiments and the activities of these enzymes increased markedly in 20 Gy irradiated groups. From these above results, functional changes of the liver were induced in all irradiated groups. Damaged liver was recovered along with time collapse after irradiation to the doses of 10 Gy and 15 Gy while no recovery was deteced within 8 weeks after irradiation to 20 Gy. These results suggest that careful attention must be paid to liver not to be included in exposure field in radiation therapy.