At partial nephrectomy there is a risk of excessive blood loss, which necessitates transfusion and also results in renal function deterioration when a vascular clamp is used. We evaluated the usefulness of a microwave tissue coagulator for partial nephrectomy for renal cell carcinoma. Partial nephrectomy was performed without renal pedicle clamping using a microwave tissue coagulator in 4 patients with a small kidney tumor. In 3 of the 4 patients partial nephrectomy was successful using a microwave tissue coagulator without renal pedicle clamping. Mean operative time and blood loss were 203 minutes and 153 ml., respectively, and there were no significant complications. In the remaining case partial kidney resection was also performed without any complications. However, nephrectomy was required due to possible incomplete tumor resection. Partial nephrectomy using a microwave tissue coagulator can be safe and successful without renal pedicle clamping. However, the insertion line of the microwave electrode must be carefully determined for resection to be curative and safe, just as when making the cut line for conventional partial nephrectomy or tumor enucleation.