ObjectiveSerum uric acid (UA) levels are reported to be decreased in patients with Parkinson's disease (PD) and multiple system atrophy (MSA). However, clinical correlates of serum UA levels are still unclear in PD‐related disorders. We conducted a cross‐sectional study to evaluate the associations between serum UA levels and disease duration, disease severity, and motor function among PD, MSA, and progressive supranuclear palsy (PSP) patients.MethodsA total of 100 patients with PD, 42 patients with MSA, 30 patients with PSP, and 100 controls were included in this study. Serum UA levels were determined, and associations among serum UA levels and disease duration, disease severity, and motor function in PD, PSP, and MSA patients were evaluated.ResultsSerum UA levels were significantly lower in male PD, MSA, and PSP patients compared with the controls, but not in female patients. Serum UA levels were negatively correlated with disease duration and severity in MSA and PSP patients, but no correlations were observed in PD patients. The serum UA levels were significantly decreased in the tauopathy group (PSP patients) compared with the synucleinopathy group (PD and MSA patients) after adjusting for age, gender, and body mass index.ConclusionWe found decreased serum UA levels in male patients with PD‐related disorders (PD, MSA, and PSP) compared with male controls, and significant correlations between serum UA levels and disease severity in MSA and PSP patients.