The progression of middle ear pathology and the mastoid hypocellularity in chronic otitis media may be influenced by the obstructive conditions in narrow aeration space of the middle ear cleft. We performed mastoidectomy surgeries in 270 cases of chronic otitis media with or without cholesteatoma which showed diploic or sclerotic types of mastoid x-ray. The pathologic condition of narrow aeration space was evaluated at the tympanic orifice of eustachian tube, tympanic isthmus, and aditus ad antrum. The obstructive degree of pathologic condition was graded as patent, partial obstruction, and complete obstruction under the microscopic examination during mastoid operation. We analyzed the obstructive degree in relation to mastoid pneumatization and compared the results between 150 cases of cholesteatoma group and 120 cases of non-cholesteatoma group, and obtained the results showing that the obstructive degree at narrow aeration spaces of middle ear cleft and mastoid hypocellularity were differed in two groups of chronic otitis media, and that the obstructive conditions in narrow aeration spaces of the middle ear cleft might cause the progression and persistence of middle ear inflammation and mastoid hypocellularity in chronic otitis media.