With the prupose to foreknow the condition of ossicles and, if possible, the hearing level attainable by tympanoplasty, prosthesis test was carried out preoperatively on 110 cases of chronic otitis media, and these results were compared statistically with the findings of the surgery and the postoperative hearing acuity. As to the prosthesis, thin patch paper or small rubber bag was employed to cover the drum perforation closely. And puretone audiometry was conducted with and without the prosthesis. The results obtained were as follows; 1) The data were investigated in each of two groups, one with disconnected ossicles, the other intact. Thereby, following two criteria were introduced, i.e. the improved hearing level better than 20 db loss or the gain of hearing more than 15 db with prosthesis. Using these criteria, the author considered, the condition of ossicles could be surmised. That is, in cases within the criteria it might be possible to diagnose that the ossicles are intact. And in the other cases without he criteria, the continuity of ossicles would be indefinite. 2) In addition, findings of the prosthesis test and hearing test after tympanoplasty were compared, an it was suggested that the prosthesis test could offer a clue to estimate possible gain of tympanoplasty.