Abstract Background The efficacy of transnasal endoscopy using an ultrathin endoscope has been reported in several studies. However, few studies regarding peroral endoscopy with ultrathin endoscopes with high resolution have been reported. This study investigates the pain alleviation of peroral endoscopy with an ultrathin endoscope. Methods Patients with a history of peroral endoscopy using a conventional, normal-diameter scope with no sedation who underwent peroral esophagogastroduodenoscopy (EGD) using a thin scope between April-July 2022 were included in this study. After the procedure, the patients completed a questionnaire evaluating pain during the examination and willingness to repeat the procedure. The physicians were surveyed regarding their level of satisfaction. The primary endpoint was patient satisfaction, which corresponded to the rate of patients who rated the thin endoscope as more comfortable or somewhat more comfortable than the previously-used, conventional endoscope. Results One hundred and forty-five patients were included in the analyses. Patient satisfaction was achieved in 86.2% (125/145) of patients. The median visual analog scale pain score was 3 (0–7) points in this study, which is significantly lower than the pain score after the previous endoscopy (5 (0–10) points; p