Many patients being followed for chronic suppuration of the middle ear have been observed to have sensorineural or mixed type hearing loss. The major cause of this bone conduction loss might be secondary to cochlear biochemical changes occuring through the round window membrane. But clinical and statistical analysis of bone conduction loss in chronic otitis media has not been exactly reported until now. The authors studied the relationship between the preoperative bone conduction hearing level and age, nature of middle ear and temporal bone pathology, extent of pathology, pneumatization of mastoid in 416 ears of chronic suppurative otitis media performed middle ear surgery at Han Yang University Hospital from March 1989 to March 1991. The results were as follows : 1) The mean bone conduction threshold was 18.24±14.86 dB. 2) In the cases of ossicular defect, bone conduction loss was greater in total destruction than in partial destruction, with, statistical significance. 3) Among ossicular defect, the incus destruction group showed more bone conduction loss than the intact incus group, with statistical significance. 4) There was no difference of bone conduction loss according to pathologic findings in middle ear cavity and mastoid antrum, but pathologic groups showed more bone conduction loss than control groups with normal temporal bone pneumatization, with statistical significance. 5) Bone conduction loss was more severe as more pathologic extension in involved area but, it was not significant statistically. 6) Comparing pneumatization of mastoid antrum and mastoid process, there was statistically significant bone conduction loss in orders of the pneumatic type, diploic type, sclerotic type, cholesteatoma cavity. 7) Bone conduction loss was predominant for a high frequency with no relation to histopathologic findings. 8) According to the frequency, the feature of bone conduction loss was horizontal when the involved lesion was small, but descending type when it was large.