We have performed partial nephrectomy using a microwave tissue coagulator for renal tumor. From July 1992 to March 2003, 9 patients (9 renal units) were operated and evaluated. They were 7 men and 2 women aged 46-77 years. One patient was indicated as chronic renal failure and others were elected indications. Tumors were 1.7-3.0 cm in diameter. In 8 cases, renal vessels did not clamped. It seemed that bleeding was less when coagulation output was not too high. Postoperative complications occurred as urinary leakage in one patient with the tumor in the renal hilum. Another patient was diagnosed as local recurrence several months after partial nephrectomy, and radical nephrectomy was carried out. It is considered that this method for small tumors is useful and less invasive.