It is unclear whether raised bone conduction thresholds in chronic otitis media are a reflection of cochlear damage, or Carhart effect, i.e. artificial elevation of bone conduction threshold due to conductive defect, or both. The purpose of this study is to discuss change of bone conduction thresholds in chonic otitis media. A total of 277 cases of unilateral chronic otitis media but without any other causes of sensorineural hearing loss were studied. Mean preoperative bone conduction differences between diseased and normal contralateral ears were not statistically significant, ranging from 9.6dB to 11.9dB across the frequencies. Post-operative bone conduction thresholds were improved in 34.1% of cases of the successful tympanoplasty type I, ranging from 9.1dB to 13.1dB across the frequencies. 33.1% to 39.1% of the subjects across the frequencies had preoperative bone conduction differences greater than 15dB. The results suggest that the bone conduction threshold in chronic otitis media is influenced by Carhart effect and cochlear damage.