목적: Any research works has not been done on stape otosclerosis in Mongolia until now and we have conducted the research in 2008-2013. 방법:We selected 41 patients /47 ears/ who were diagnosed of having otosclerosis with conductive hearing loss, no middle ear infection through the comprehensive ear and hearing examinations in EMJJ Clinics between 2007 and 2013. 결과:As for age, out of 41 patients involved in the research by age 5 patients were 8-15 years old 5 people, 6 patients were 16-25 years old, 7 patients were 26-35 years old, 20 patients were 36-45 years old, 3 patients were 46-60 years old. 35 patients (85.4%) were female while 6 patients (14.6%) were male. Patients were classified by hearing loss level and type II level hearing loss 8,7%, III level hearing loss 37,4%, IV level hearing loss 4,8% with hearing aid, II level 64%, III level 49,7%, IV level 79,0% sensorineural hearing loss and 12,9%-33,3% of all patients had mixed hearing loss, which showed the need for improving hearing (Chart 4). 5 patients who have hearing loss in both ears and 36 patients with hearing loss in one ear have been diagnosed of otosclerosis. K-Piston titanuin prosthesis (KURZ company, Germany) with 0,4 wide, 4,0 wide 4,0 long was used for 36 ears and -Piston titanuin prosthesis (KURZ company, Germany) with 0,6 wide 4,5 long were used for 10 ears and during the surgery otosclerosis was confirmed to be a diagnosis. After 120 days of the surgery, the hearing of 33 patients improved completely, bone conduction became 2000 Hz at 4000 Hz frequency 12-15 dB, average of air conduction 15,410,1 dB, bone-air gap 10,43,1 dB for 5 people, and bone conduction 2000 Hz-4000 Hz, at 8000 Hz frequency 20-40dB, air conduction became 25-45dB 10,45,1db for 9 patients and all patients had no hearing loss except for 4 people who still had tinnitus. 결론:After 120 days of the surgery the hearing of 33 patients improved completely,air conduction was 2000 Hz, at 4000 Hz frequency average 10-15dB