This paper proposes a surgical assistance scheme, which enables to locate small cancer lesion using RFID (Radio Frequency Identification Tags). State-of-the-art systems for endoscopic surgery are expected to be capable of finding very small cancer lesions in the diagnostic imaging although such small lesions have been difficult to be identified for excision through an endoscope. To find such small lesions surely during endoscopic excision surgery, a new endoscope supporting system is desired. In our proposed system we use a RFID tag to label each small lesion part during diagnostic imaging, then use a RFID tag signal sensor antenna at the time of an operation and supports discovery of a lesion area. In this report, it is possible to estimate a small lesion area using the RFID tag system, which is composed of the signal sensor antenna and RFID tags. The measurement system using a RFID tag and 4 sensor-antennas was made as an experiment, and the experiment using phantom was conducted. As a result, the difference with a theoretical value of less than 40 mm of distance of a RFID tag and a sensor antenna and the value acquired in 10 mm of phantom thickness was less than 2 mm. Furthermore, the value acquired when moving the spatial relationship of a RFID tag and a sensor antenna 20 mm each in x, y and z was verified, and it was shown clearly that errors are a minimum of 2.6 mm and a maximum of 22 mm.