Acid in the mouth after eating is considered a high possibility of gastroesophageal reflux disease. After eating, the stomach is poorly emptied and food containing stomach acid flows back upward into the mouth, causing the mouth to become acidic. In this case, gastroscopy is needed to clarify the situation. After the diagnosis is confirmed, the following adjustments should be made: First, the diet should be less frequent, less oily and spicy food, and abstain from alcohol. Second, it is recommended to take a proper walk after meals, and the foot of the bed on the side of the head can be slightly elevated when sleeping to reduce gastric reflux. If the above dietary and behavioral modifications do not work well, medications such as mosapride citrate plus omeprazole or lansoprazole can be considered for a general course of treatment of three weeks or more.