objective:to investigate the effect of vagus nerve on first－phase insulin secretion. Methods:five healthy beagle dogs were anesthetized and cut off anterior vagal trunk and post vagal trunk of vagal celiac trunk. Intravenous glucose tolerance test and the continuous infusion of glucose via the carotid artery were performed in five beagle dogs prior to and after truncal vagotomy. Blood samples were collected from jugular vein of opposite side each time at the 0,1,2,4,6 and 10 min to measure plasma insulin and blood glucose levels. Results:during intravenous glucose tolerance test,first－phase insulin secretion obviously dropped after truncal vagotomy compared to prior(p < 0.05). But blood glucose failed to show significant difference before and after truncal vagotomy. The continuous infusion of low dose glucose via the carotid artery failed to induce any change in vein glucose level but caused an increasing of insulin secretion. It reached the peak at 2~4 min. Insulin secretion obviously dropped after truncal vagotomy(p < 0.05). Conclusion:the central nervous system may play a role in regulating first－phase insulin secretion,which is mediated by vagus.