Tonsil and adenoid hypertrophy was the important factor in the occurrence of serous otitis media in children. Impedance audiometry was performed as a routine clinical examination in a consecutive series of 75 cases with tonsil and adenoid hypertrophy. In order to observe the relationship of the hypertrophy of tonsil and adenoid with middle ear function, authors classified into 3 categories of T & A group in relation to hypertrophy status and normal group. This study was aimed to obtain the difference in tympanometry type, acoustic reflex threshold and percentage of absent acoustic reflex. The result were summarized as follows ; 1) Among 100 cases, M : F ratio was 1.4 : 1 and 5-7 age group was most common. 2) Chief complaint of T & A group was the most common in frequent U.R.I. symptoms. 3) Distribution of abnormal tympanogram type was increased as the hypertrophy was greater : 24.0% in the normal group, 34.0% in the mild group, 50.0% in the moderate group and 70.0% in the severe group. 4) Abnormal tympanogram type, B and C types were increased in relation to hypertrophy of tonsil and adenoid. 5) Distribution of abnormal tympanogram type in relation to age was most common in 3-6 age group. 6) Acoustic reflex threshold revealed no difference in relation to hypertrophy status. 7) The incidence of absent acoustic reflex was higher in T & A group.