This case report describes a patient with obstructive sleep apnea (OSA) who could not receive oral appliance therapy because of temporomandibular disorders and was instructed to perform tongue rotation exercises. The patient’s maximum tongue pressure, lip-seal strength, and subjective sleep quality improved post-intervention. Furthermore, apnea-hypopnea index and sleep architecture were improved after exercise compared with the baseline. These results suggest that tongue rotation exercises can improve not only oral function but also respiratory function during sleep and, thus, may be meaningful to introduce as an adjunctive therapy for OSA with impaired oral function or intolerance to conventional therapies.