Objective To evaluate the consistency between syringe suction using 50 mL injection syringe and ultrasound measurement of gastric residual volume (GRV) at different positions and feeding patterns, and to provide reference for accurate assessment of GRV. Methods A total of 137 patients with nasogastric tube were recruited to measure their GRV through syringe suction at three different positions including left lateral position, supine position and right lateral position at three different feeding patterns:fasting more than 8 hours, 4 hours after continuous feeding and 4 hours after intermittent feeding. At the same time, ultrasound measurement of GRV at right lateral position was also conducted as gold standard. Bland-Altman method and regression analysis were performed to determine the level of agreement. Results Bland-Altman method showed excellent agreement between syringe suction and ultrasound assessment at fasting pattern at all 3 positions,with 95% of the data points lying within the agreement interval (±1.96 s of the mean difference). Acceptable agreement of the two methods was also found at right lateral position during continuous feeding and intermittent feeding, with 95% of the data points lying within the agreement interval. Conclusion High consistency between syringe suction and ultrasound assessment of GRV was verified at all 3 different positions when patients were fasting more than 8 hours. However, consistency of the two methods during enteral feeding was only found at right lateral position.