Severe trismus often causes significant compromise in quality of life due to severe impairment of oral functions. Treatment of trismus needs to be tailored to the cause. Here, we report the case of a successful treatment for severe trismus after maxillectomy using coronoidectomy, condylectomy, and vascularized fibula flap transfer. A 65-year-old female suffered from severe trismus due to temporomandibular joint (TMJ) ankylosis and contracture of the oral mucosa 5 years after partial maxillectomy for a squamous cell carcinoma. Surgical release including a masticatory muscle myotomy, a coronoidectomy, and a condylectomy was performed. After the surgical release, the size of the defect of the oral mucosa was 5 × 10 cm. Then a free vascularized fibula osteomusculocutaneous flap with a 5 × 12 cm skin paddle and a 5 cm fibula bone was transferred. The fibula bone was fixed to the hard palate and zygomatic body. The intraoperative final interincisal distance achieved 30 mm. The postoperative course was uneventful and the free fibula osteomusculocuateous flap survived completely. At 32-month follow-up, although the interincisal distance had regressed to 25 mm, the patient maintained an improvement in the patient's quality of life. Combined treatment with coronoidectomy, condylectomy and free tissue transfer may be effective for severe trismus having multiple causes: oral mucosa contracture and TMJ ankylosis.