We have examined the possibility of the percutaneous microwave coagulation therapy (PMCT) guided by CT for the lung tumors. Microwave coagulation therapy was performed for the normal lung tissues of beagles and human lung after resection of central type lung cancer in the conditions of power : 20, 40, 60W and treatment time : 1, 2, 3, 4 min at the each power. We investigated the diameter of maximum coagulation area and histopathological changes of normal lung tissue by H-E and Elastica von Gieson stain. Maximum coagulation of 22 mm was obtained in the condition of 60W, 4 min. for the normal lung of beagles and 25 mm was obtained in the condition of 40W, 3 min and 60W, 3 min for the resected normal human lung. Histopathological examination showed the coagulating changes, e. g., small picnotic nuclear, pooling of exudate in alveolar cavity, coiling of elastic fiber, abruption of vessel. In clinical case, we performed PMCT for the patient with lung metastatic tumor 2.0 cm in diameter from colon. More than 90% of tumor necrosis was observed by H. E. stain. Our results showed the utility of PMCT for the inoperable lung tumor or small peripheral lung tumor.