Objective Melatonin is effective for treating patients with rapid eye movement sleep behavior disorder (RBD). Ramelteon, a novel hypnotic, acts as a melatonin receptor agonist. In the current study, we investigated the effects of ramelteon on sleep disorders, including RBD, in patients with Parkinson's disease (PD). Methods We evaluated 35 patients from multiple centers with idiopathic PD accompanied by sleep disturbances (age: 69.1±11.1 years; 17 men, 18 women; PD morbidity: 6.9±5.7 years; Hoehn & Yahr stage: 2.5±0.8; levodopa dose equivalent: 561±401 mg/day). The patients received 8 mg of ramelteon before sleep once daily for 12 weeks. Motor and sleep symptoms were evaluated both before and after ramelteon administration. Results Of the 35 patients enrolled in this study, 24 (68.6%) were diagnosed with probable RBD (pRBD) using the Japanese version of the RBD screening questionnaire. Ramelteon administration reduced the severity of sleep disturbances in patients with PD. It also lowered scores on the Japanese version of the RBD questionnaire in patients with PD and pRBD. Conclusion Ramelteon may have beneficial effects on sleep disturbances, especially on RBD in patients with PD.