Bitterness in the mouth after eating needs to be considered if there is a problem with the mouth. Certain abnormal infections of the mouth, such as gingivitis, periodontitis, and mouth ulcers, may cause the symptoms of bitter mouth after eating. It is also important to consider whether there is bile reflux into the mouth, which can cause the symptoms of bitterness in the mouth. This is because it causes a large excretion of bile for digesting food after eating. If there is a corresponding biliary tract disease or the pylorus of the stomach is relaxed, a large amount of bile excreted into the intestine does not go down, but with upward reflux into the stomach and into the mouth, thus causing bitterness in the mouth. In this case, it is necessary to take in more water and to move properly after eating in order to promote the bile to flow downward instead of backward. In addition, those who have biliary tract diseases should also be given appropriate treatment, and bile reflux can be effectively relieved only if the corresponding diseases are cured.