Various clinical reports have been focused on the effetiveness of high-resolution computed tomography(CT) of the temporal bone for detection of bony destructive lesions in patients with cholesteatoma. But studies of the effectiveness of CT for soft tissue pathologies of the middle eat cleft are relatively rare. We studied the effectiveness of the temporal bone CT for the evaluation of the aeration condition of the narrow aeration spaces such as eustachian tube orifice, tympanic isthmus, and aditus ad antrum which are important for the normal middle ear function. During the tympanomastoid operations in 139 cases of chronic otits media with or without cholesteatoma, we investigated whether these aeration space of the middle ear cleft are obstructed or not. After then, we compared the aeration conditions of the operative findings with those of CT findings. CT revealed that diagnostic predictability of the aeration condition in the narrow areation spaces was between 60% to 68.6% in non-cholesteatoma group and between 69.2% to 75% in cholesteatoma group. And even in cholesteatoma group, diagnostic predictability at the level of tympanic isthmus and aditus ad antrum was significantly higher in the cases of involvement of cholesteatoma at these levels in the cases of no involvement.