Gastroesophageal reflux disease (GERD) is a condition that develops when reflux of stomach contents causes troublesome symptoms and/or complications. It is the most frequent problem in upper gastrointestinal tract in outpatient clinic and contributes substantially to morbidity and to costs. Endoscopy is a widely used modality for the diagnosis and classification of GERD, and the extent of esophageal mucosal breaks on endoscopy can be assessed. However, because more than half of patients with GERD reveal no visible abnormality on conventional endoscopy, it is possible that minute mucosal changes are underestimated by conventional endoscopy due to the limitation of visual ability.