Non-erosive reflux disease (NERD) is characterized by the absence of esophageal mucosal damage during upper gastrointestinal endoscopy, despite the presence of typical symptoms of gastroesophageal reflux, such as heartburn and acid reflux. In addition, acid reflux is known to have only a minor effect on the pathophysiological mechanism of NERD. For this reason, NERD patients who receive proton pump inhibitors (PPIs), which are the first-line therapy for GERD, show a low symptom improvement rate, and almost 50% of NERD patients fail to respond to standard acid-suppression therapy that uses PPIs. Therefore, it is important to evaluate the pathophysiology of NERD and to create the therapeutic strategy for each patients.