Although otosclerosis is essentially a middle ear disease, patients with this disease often exhibit mixed hearing loss. This discrepancy is thought to be explained by the following mechanism: the resonance of the ossicular chain is disturbed by the fixation of stapes, leading to the attenuation of inertial bone conduction. The bone-conduction hearing level usually recovers after stapes surgery. We herein studied the change in air- and bone-conduction hearing after stapes surgery in patients with otosclerosis. Six consecutive patients with otosclerosis who underwent stapes surgery in our department were enrolled. They were 2 men and 4 women, ranging in age from 16 to 74 with an average of 57.2 years. Stapedotomy was performed in 5 patients, and the other patient underwent partial stapedectomy. Their pure tone hearing levels of air and bone conduction were measured before and after surgery. In the air conduction, the hearing levels at 125, 250, 500, 1000, 2000, and 4000 Hz significantly improved after surgery, but showed no significant change at 8000 Hz. On the other hand, in the bone conduction, the hearing levels at 500 and 1000 Hz significantly improved after surgery, whereas those at 250, 2000, and 4000 Hz showed no significant change. The recovery of the bone conduction hearing at 500 and 1000 Hz is explained by the resonance of the ossicular chain. However, the unimproved bone conduction hearing at 2000 Hz is unexplainable, and remains to be further investigated in future studies.