To analyze the pattern of bone conduction losses in chronic otitis media, and to correlate this findings with clinical and pathological changes in human and animal model, 187 ears were selected for this study following careful evaluation of other possible causes of sensori-neural hearing losses in 233 tympanomastoidectomy ears operated in the last one year A histopathological study was done in 5 guinea pigs with natural otitis media. A significant difference in bone conduction threshold was observed between the normal and diseased ears in unilateral cases, and a significant interaction was noted between 2 KHz. and 4 KHz. (p<0.01). Using one way analysis of variance, mean bone conduction was compared with the duration of disease. We observed a significant difference between each group of duration (p<0.05), except between 11-15 and 16-20 years group. The degree of bone conduction loss is related to the round window obliteration group (p<0.01), and stapes destruction group (p<0.01) at each frequency. Cholesteatoma cases are less insert to bone conduction loss if there is no frank invasion of the inner ear. In the histopathological study of natural otitis media in guinea pigs, the changes in the round window area and the cochlea would explain high frequency loss in the process of chronic otitis media.