OBJECTIVE: To determine whether photobiomodulation therapy by class IV Multiwave Locked System laser treatment could relieve symptoms in patients with Bell's palsy with a duration of greater than 8 weeks. METHODS AND METHODS: This randomized controlled trial from May 2021 to April 2023. Patients were eligible who had Bell's palsy with a duration of greater than 8 weeks on out-patient department of otorhinolaryngology in Beijing Tongren Hospital. The photobiomodulation group received class IV Multiwave Locked System laser treatment for 3 times per weeks, a total of 6 months. The control group received the same Multiwave Locked System treatment procedure except the laser parameter. The primary outcome measures comprised House-Brackmann facial nerve grading system, Sunnybrook facial grading system, Facial Clinimetric Evaluation Scale. Secondary outcome measures comprised Electroneurography, Electromyography, and the Blink Reflex.