Tonsillectomy and adenoidectomy(T & A) are one of the most important operations for children in the otolaryngologic field. The authors attempted to know indirectly a certain effect to restore ventilatory function of eustachian tube after T & A. In 38 T & A children(76 ears) during the period of June 1, 1982 through Mar. 31 1983, impedance audiometries(Tympanogram, static compliance, and acoustic reflex threshold) were performed before and 10 weeks after the operations. All the children did not have perforation of tympanic membrane and did not undergo myringotomy, middle ear intubation, or antrostomy. In tympanogram, 49 ears of type A did not change in 47 ears but 2 ears became type C. Nineteen ears of type B did not change in 12 ears but 7 ears to type A. All the 8 ears of type C changed to type A. Static compliance and acoustic reflex threshold also showed relatively significant differences in the changed cases.