This article discusses Gastroesophageal Reflux (GER), an entry of gastric content into esophagus with more than once regurgitation a day, which often happens to a four-month-old child. The main cause of GER is the imperfection of both the tonus muscle of the lower esophageal sphincter and the length of esophagus. The diagnosis of GER can be made by clinical examinations as well as laboratory and radiology tests, which may result in different kinds of GER: hiatus hernia, achalasia, hypertrophy congenital of pyloric stenosis, duodenal atresia, meconium ileus. The therapy of GER can be a) non-pharmacological, e.g. by raising the child’s head to be higher than its body position; no more feeding 2 hours before the child sleeps; avoiding food that can trigger GER; giving no milk by the child’s sleeping time; b) pharmacological, e.g. by giving antacid, prokinetic medicine, histamine receptor H2 antagonist, and inhibitor pump proton; and c) surgical, which should be the last choice.