Relief of adverse events induced by chemotherapy is an important issue for patients, especially those with a poor prognosis, such as with pancreatic cancer. There are no reports of the relationship between gastroesophageal reflux disease (GERD) and chemotherapy, so we investigated the incidence of chemotherapy-induced GERD in patients undergoing treatment with gemcitabine or S-1 for pancreatic cancer and the effect of sodium rabeprazole (RPZ), a proton-pump inhibitor. GERD was diagnosed in 40% of the patients according to the Frequency Scale for Symptoms of GERD score, and RBZ therapy significantly improved their symptoms.