Recent advancement in the research of GERD has revealed that endoscopy negative GERD may not be a milder form of erosive GERD and may have different pathogenesis. We have previously proven that hypersensitivity to the acid of the esophageal mucosa plays an important role in its pathogenesis. Regarding the mechanisms for the esophageal hypersensitivity, we hypothesized that the tight junction proteins of the esophageal mucosa are fully or partially impaired in GERD patients. Accordingly, we immunohistologically studied the expression of various tight junction proteins using the rat reflux esophagitis model. The results demonstrated that the several kinds of tight junction proteins are expressed differently in the various parts of esophagus and their expression altered according to the development of reflux esophagitis.