Treatment with Tranilast of 45 patients (87 ears) with secretory otitis media was studied. Tranilast was administered orally for at least 1 month. The evaluation of its effectiveness was based on changes in subjective symptoms, tympanic membrane findings, hearing level, and tympanometry. Subjects were divided into three groups: allergy group (group I), nonallergy group (group II) and deformity-disorder group (group III). The respective percentages of Tranilast efficacy for these three groups were 46.2%, 42.1%, and 10.0%, respectively. Equivalent effectiveness was demonstrated whether or not allergies were present. After Tranilast administration, the drug and its metabolites were found in MEE samples from all the patients. Anaphylatoxin (C3a, C5a) activities in the MEE were shown to decrease gradually after Tranilast administration. Tranilast may be effective for treating secretory otitis media because it directly suppresses anaphylatoxin present in middle ear effusion.