Radiological and clinical evidences indicate that hyperthermia combined with irradiation produce a significant improvement in therapeutic effect of cancer. The experiences obtained from 90 rats' kidney. A single dose of irradiation ranged from 6 Gy, 8 Gy and 10 Gy was delivered on the rat's kidney. The combined therapy group had the same irradiation after hyperthermia at 42-44 degree Cfor 30 minutes. Microscopic examination and calculation of thermal enhancement ratio were carried out, and the results were as follows: 1. In the group of hyperthermia alone, there were moderate glomerular congestion and mild tubular degeneration on light microscopic examination. 2. In the group of irradiation alone, tubular degeneration was noted in 6 Gy irradiation and its severity was increased along with radiation dose. 3. In the group of hyperthermia combined with irradiation, tubular degeneration and necrosis were appeared in 6 Gy and 10 Gy irradiation, respectively. 4. On electron microscopic examination, proximal convoluted tubular and glomerular changes in irradiation group were similar to that of combined with hyperthermia, and its severity was increased along with observation periods. 5. Thermal enhancement ratio(TER) was 1.0 after evaluation of histipathologic changes in rat's kidney with combination therapy.