In order to clarify the cause of the constriction of the eustachian tube during swallowing that is often seen in patients with otitis media with effusion, video endoscopy of the pharyngeal orifice of the eustachian tube was performed and superimposed with videograms of the tubal airflow and resistance, which were simultaneously examined by the forced response test. In children with otitis media with effusion (17 ears), when the eustachian tube constricted on the videogram on swallowing, the tubal orifice was found to be squeezed between an elevated soft palate and a hypertrophied adenoid (7/17), squeezed between an elevated soft palate and edema of the posterior lip (7/17), or blocked by nasal discharge (5/17). In adults with otitis media with effusion (7 ears), edema of the posterior lip (5/7) was the main cause of the constriction of the tubal orifice during swallowing. Inflammation in the nasopharynx and the pharyngeal portion of the eustachian tube was considered to be closely related to the tubal constriction, which represents a considerable part of the cause of tubal ventilatory dysfunction in otitis media with effusion.