ObjectiveEpisil® is a bio adhesive barrier-forming oral liquid gel that has been used in recent years to relieve pain of oral mucositis (OM) with radiotherapy (RT) or chemoradiotherapy (CRT) in head and neck cancer (HNC) patients. We conducted a retrospective analysis of the clinical effects of Episil® on OM in these patients.Study designBetween June 2018 and May 2020, 65 patients with HNC were treated with RT or CRT at our hospital.ResultsThe median total RT dose was 50 Gy (range, 30–70 Gy) and the completion rate was 63/65 (97%). The median time to OM resolution was 47 (6–90) days and was significantly longer (53 [27–90] days) when the total RT dose was ≥51 Gy (P< 0.001). Episil® was used in 26 patients. Among them, 10 discontinued its use due to ineffective pain relief, usage difficulties, and taste intolerance. The median duration of use was 30 days and was significantly longer (34.5 days) (P< 0.001) when patients experienced pain relief at treatment initiation.ConclusionAlthough Episil® has been shown to be effective in improving the pain of OM caused by RT for HNC patients, and medical professionals are required to give careful attention to each patient.