The dumping syndrome has been a known complication of gastric surgery in adults, but it is recognized as a very rare disease in the pediatric population, especially in Korea. We report a case of dumping syndrome in a 10-month-old infant, who underwent Nissen fundoplication for the treatment of gastroesophageal reflux(GER). He was admitted because of aspiration pneumonia, and diagnosed as GER by 24-hour ambulatory esophageal pH monitoring test. For the treatment of GER, Nissen fundoplication was performed. After the operation, symptoms occurred within 30 minutes of meals, such as diaphoresis, palpitation, weakness, abdominal fullness, nausea, and diarrhea. The gastric emptying scan showed very rapid gastric emptying. His oral glucose tolerance tests revealed early-onset hyperglycema followed by delayed-onset hypoglycemia, which was the characteristic finding of the dumping syndrome. We introduced uncooked cornstarch to resolve symptoms and maintain the serum glucose level. After the feeding of uncooked cornstarch, his symptoms subsided and normal oral glucose test was restored. After the six months of treatment, his weight and height were increased dramatically from below 3 percentiles up to the normal range. The dumping syndrome should be considered when an infant suffers from the feeding difficulties after the gastric surgery like Nissen fundoplication, and the diet therapy including uncooked cornstarch could be applied as an effective measure.