Abstract: A Microprocessor controlled Relay is between and in series with the Electro-Surgical Unit and the NiCr loop, to control the output power of the E.S.U. during the operation of Transurethral Resection. The predetermined parameters may input to the Microprocessor for precision control of the E.S.U.. A current probe is connected to the output cable of the E.S.U. to take the variety of the output current of the E.S.U.. The E.S.U. output power will vary according to the variety of the load. By the differences of tissues, the differences of inclusions make the consistency and conductivity vary. The differences of conductivity make the load vary during operating procedure of Transurethral Resection. In other words, the control system can distinguish what tissue is resected according to the variety of the output power of the E.S.U..