A primary mass lesion arising from the tympanic membrane is extremely rare. The authors report a patient of extensive fibrosis within the tympanic membrane in a 65-year-old woman who did not have a history of ear infection. The patient complained of slow progressing hearing loss on the left side without otorrhea or otalgia. Otoscopic examination showed a thick tympanic membrane with whitish mass-like bulge, and pure-tone audiometry revealed conductive hearing loss. The lesion was totally resected, and final findings of a histopathologic examination revealed extensive fibrosis with subsiding inflammation within the tympanic membrane. Fibrosis within the tympanic membrane may present with slow progressing conductive hearing loss and should be considered a possible differential diagnosis of mass lesions in the tympanic membrane.