The surgical goal in the treatment of chronic ear disease is to obtain a safe, dry ear with functional hearing. To obtain a good functional result in tympanoplasty, it is one of the essential prerequisite to have an aerated middle ear space. The purpose of this study is to elucidate the factors that control the formation of the sound middle ear space at the tympanoplastic procedure. 49 ears were retrospectively reviewed and analyzed using acoustic immitance, which was checked postoperatively at least 6 months later. Postoperatively Type A tympanogram was seen more frequently in chronic otitis media without cholesteatoma(60%), without attic block(93%), and without mucosal disease which should be removed during operation(63%)(p<0.01). This study shows that pathologic status of middle ear and mastoid and attic block are important to the formation of aerated middle ear space postoperatively.