Abstract Purpose Rapid eye movement (REM) sleep behaviour disorder (RBD) is an important indicator of underlying synucleinopathies. However, the frequency of RBD in tauopathies such as progressive supranuclear palsy (PSP) remains unclear. In this study, we compared RBD-related symptoms and polysomnographic (PSG) findings between patients with PSP and those with Parkinson’s disease (PD). Methods We conducted clinical interviews of 20 patients with PSP, 93 patients with PD and their caregivers regarding RBD-related symptoms, and conducted PSG recordings on all the subject patients. We then compared the clinical backgrounds, PSG parameters, and frequency of RBD-related symptoms between the two groups. Results PSP patients had more severe symptoms of Parkinsonism and cognitive impairment, and took lower doses of dopaminergic agents compared with PD patients. The PSP group had lower values for both estimated total sleep time and sleep efficiency on PSG compared with the PD group (p = 0.002, p = 0.021, respectively). The PSP group also included a significantly smaller number of patients having REM sleep without atonia (RWA) compared with the PD group (n = 5, 20.0% vs. n = 56, 60.2%, p = 0.003). None of the PSP patients were experiencing RBD-related symptoms at the time of the investigation, while 30 PD patients (32.3%) had RBD-related symptoms. Discussion The existence of RWA as well as RBD-related symptoms was less frequent in patients with PSP versus patients with PD. Differences in brain stem pathology and/or disease course between the two disorders might influence this difference.