Many of the patients being followed for chronic suppuration of the middle ear were observed to have sensorineural or mixed type hearing loss. The major cause of this bone conduction loss might be secondary to cochlear biochemical changes occurring through the round-window membrane. But, clinical and statistical analysis of bone conduction loss in chronic otitis media has not been fully reported until now. Author studied the relationship between the preoperative bone conduction hearing acuity and age, duration of disease, presence of drainage, nature of pathology, extent of pathology, size of tympanic membrane perforation, pneumatization of mastoid in 187 ears of chronic suppurative otitis media who has had middle ear surgery at Dept. of Otolaryngology Han Yang University Hospital from May 1986 to June 1988. The result were as following ; 1) Mean bone conduction threshold of chronic otitis media was 19.92±11.77 dB. 2) Bone conduction loss was increased with older age, but there was no significant difference because presbycusis occupational hearing loss, drug and duration of disease were not ruled out. 3) Bone conduction loss was increased with the increase of duration of the disease. 4) Mean bone conduction threshold was 16.61±10.93 dB for those ears with no drainage, was 20.56±11.85 dB for those ears with active drainage. Bone conduction loss was greater in cases of active drainage than no drainage. 5) There was no relationship between bone conduction threshold and histopathologic type tissues in middle ear and mastoid cavity found during middle ear surgery in chronic suppurative otitis media. However the degree of bone conduction loss was greatly related to the extent of pathology. 6) Bone conduction loss showed increasing trend with the size of tympanic membrane perforation. 7) Compared with development of mastoid pneumatization in chronic purulent otitis media, bone conduction loss showed increasing trend with undeveloped mastoid pneumatization.