Objective To measure the serum uric acid concentration in patients with Parkinson's disease (PD) and examine the relationship between serum uric acid level and cognitive impairment in PD patients. Methods Eighty-seven PD patients and 81 control subjects were recruited. Their cognitive functions were evaluated using the Mini-Mental State Examination, Wechsler Intelligence Scale, and Wechsler Memory Scale; the motor aspects of the disease were assessed using section Ⅲ of the Unified Parkinson Disease Rating Scale, and the severity of the disease was determined using the Hoehn-Yahr (H-Y) scale. Serum uric acid concentration was measured and then was compared between PD patients and controls and between the patients with different H-Y stages of PD. Linear regression analysis was employed to analyze the correlation between serum uric acid level and neuropsychological performance. Results Serum uric acid level was significantly lower in the PD patients than in the controls (P<0.05). There was no significant difference in serum uric acid level between patients with H-Y stage < 3 PD and those with H-Y stage ≥3 PD (P>0.05). The multiple linear regression analysis revealed no correlation between serum uric acid level and neuropsychological performance (P>0.05). Conclusions Decrease in serum uric acid level may be associated with PD, but it may not be associated with cognitive impairment in PD patients.