We usually experience bone conduction impairments in chronic otitis media, but it is unclear whether raised bone conduction thresholds are a reflection of cochlear damage or Carhart effect ; a artificial elevation of bone conduction threshold due to conductive defect, or both. The purpose of this study was to discuss the influence of artificial elevation of bone conduction threshold in chronic otitis media and estimation of Carhart effect. A total of 137 cases of tympanoplasty type I or type II with unilateral chronic otitis media without any other causes of sensorineural hearing loss were studied. Bone conduction thresholds were improved in 46.9% of 49 cases that had preoperative difference of more than 10dB between diseased and contralateral healthy ears at 2 or more frequencies. The average of improved threshold had no statistical differences between frequencies. The maximum was 11.9dB at 1000Hz, and the minimum 8.8dB at 250Hz. The results suggest that the bone conduction threshold in chronic otitis media is influenced by artificial elevation due to conductive defect and can be improved by reconstructive surgery.