Background: Many studies have addressed chronic dysphagia resulting from chemoradiotherapy for head and neck cancer (HNC) because of its severity, but changes in the swallowing function during chemoradiotherapy has been rarely reported. This study aimed to elucidate the changes in the swallowing function during chemoradiotherapy for HNC. Methods: From April 2018 to July 2020, 20 patients who underwent definitive or postoperative chemoradiotherapy at our hospital for head and neck squamous cell carcinoma were evaluated by flexible endoscopy with the Hyodo scoring system for swallowing, the Penetration-Aspiration Scale (PAS), and the Functional Outcomes Swallowing Scale (FOSS). Results: Assessments at the start of treatment, at 40 Gy, and at the end of treatment yielded these mean values: Hyodo score-0.39, 1.22, and 2.56; PAS-1.00, 1.05, and 1.5; FOSS-0.2, 0.55, and 1.1, respectively. The Dunn multiple comparison test was used for analysis to determine significance (P < 0.05). The Hyodo score and FOSS were significantly increased at the end of treatment versus initial evaluation; however, score was maintained at a tolerable level for oral intake. PAS did not show a significant increase. Conclusion: In conclusion, changes in the swallowing function during chemoradiotherapy for HNC were mild, and swallowing function was maintained at a tolerable level for oral intake.