BACKGROUND New modalities for local treatments that destroy tumor effectively but which are less invasive and less damaging to normal lung tissue must be developed for patients who are unable to undergo even video-assisted thoracic surgery (VATS) due to poor cardiopulmonary function, severe adhesion, or advanced age, etc. We evaluated the use of microwave coagulation therapy (MCT), which has been used successfully for coagulation of hepatic tumors, in normal canine lung tissue to evaluate its efficacy and safety. METHODS Measurements of thermal response and coagulation area and histological examinations after microwave coagulation were performed in normal canine lung tissue. RESULTS The temperature in normal canine lung tissue increased to 90-100 degrees C at 5 mm from the electrode after 60 s and 70-80 degrees C at 10 mm after 90 s at 40 or 60 W. The coagulation area was approximately 20 mm in diameter at 40 W and 60 W. Histological analysis demonstrated thickening of collagen fiber shortly after coagulation, stromal edema and granulation tissue after 3 months, and, finally, scar tissue was seen after 6 months. CONCLUSIONS Microwave coagulation therapy (MCT) is a useful modality for minimally invasive therapy in peripheral lung tumors.