In this paper, we suggest the ultrasonic-assisted technique of the thickness determination system on low anterior resection. We propose a technique for thickness determination of the intestine for low anterior resection using the ultrasound, whose center frequency is 15 MHz. Low anterior resection is one of the operative methods for rectum cancer. We determine the intestine thickness from ultrasonic waves using fuzzy inference. We performed the experiment using the biological phantom and the large intestine of the pig as a target object. As the results, we calculated the object thickness with the average absolute error of 5.67%.