In this study, we analyzed the clinical features, diagnostic criteria, treatment, and outcome of atypical bilateral progressive hearing loss associated with myeloperoxidase-antineutrophil cytoplasmic antibody (MPO-ANCA). The evaluation was made by audiogram and laboratory data in 6 cases treated at Hokkaido University Hospital. We measured MPO-ANCA by enzyme-linked immunosorbent assay; the result was positive in all cases. The hearing loss developed bilaterally and progressed to total deafness within several weeks. The onset of hearing loss was not simultaneous in the 2 ears. Methylprednisolone pulse therapy was effective in 9 ears. Three ears showed no improvement; 2 of the 3 ears had already exhibited total deafness at the first visit. After the treatment, the titer of MPO-ANCA decreased in all patients. The level of MPO-ANCA should be tested in patients with bilateral progressive hearing loss of unknown origin and can be used as a marker of the disease's activity.