We have conducted an experiment to examine the effects of a truncal vagotomy on the gallstone formation. Chosen for this experiment were ICR male mice that were given an abdominal vagotomy. While the postoperated mice were on a cholesterol-free diet, we found that, due to the vagotomy, the mole fraction of the cholesterol in the mice's gallbladder bile increased, as did the total protein concentration in their bile. When being fed foods to promoted a gallstone, the postoperated mice clearly demonstrated a higher rate of gallstones formation than without the vagotomy, and while the cholesterol concentration in their bile did not show a significant increase, total protein concentration did increase significantly. The rate of a biliary infection also increased. Considering the above, we have concluded that a truncal vagotomy is a factor that promotes the gallstone formation.