Sleeve gastrectomy, which is based on reducing the size of the stomach, is one of the most successful bariatric surgeries and is yet to be standardized. One of the reasons is the lack of a method to obtain an accurate remnant stomach volume. The weight loss obtained postsurgery is highly correlated with the remnant stomach volume. Therefore, it is important to get consistently an accurate remnant stomach volume to be able to compare sleeve gastrectomy with other surgeries and in order to predict the weight loss. In addition, the measurement of the pyloric pressure is important for understanding the mechanism of weight loss and predicting complication postsurgery. A surgical assistive device for sleeve gastrectomy surgery is presented in this paper. The purpose of this instrument is to assist surgeons in obtaining an accurate remnant stomach volume and in measuring the pyloric pressure. The device consists of several inflatable compartments controllable by the surgeon. Prototype laboratory test results gave an accuracy of 96.7% and a repeatability of 97.6% for different desired volumes using air for compartment inflation, and an accuracy of 96.3% and a repeatability of 98.4% for different desired volumes using water for compartment inflation. The pressure measurement accuracies obtained are 96.8% using air and 99.7% using water. It is worth noting that these accuracies are expected to differ when the device is tested in vivo.