This study sought to determine the efficacy of interpositional arthroplasty with temporalis muscle and fascia flap in the treatment of unilateral temporomandibular joint (TMJ) ankylosis in adults. This retrospective study of seven cases evaluated the postoperative results of interpositional arthroplasty on temporalis muscle and fascia flap in adults. The operative protocol for unilateral TMJ ankylosis entailed, (1) resection of ankylotic mass, (2) intraoral ipsilateral coronoidectomy, (3) contralateral coronoidectomy when necessary, (4) interpositional tissue transfer to the TMJ with temporalis muscle and fascia flap, (5) maxillomandibular fixation (MMF), and (6) early mobilization and aggressive physiotherapy. The results of this protocol were encouraging, while the functional results of interpositional arthroplasty on temporalis muscle and fascia flap were satisfactory. The findings of this study support the use of temporalis muscle and fascia flap in adult patients with unilateral TMJ ankylosis. Early postoperative initial exercise, physiotherapy, and strict follow-up play an important role in preventing postoperative adhesions.