Objective To study the relationship between level of plasma glucose and cognitive function in patients with Parkinson's disease.Methods Two hundred PD patients were assessed cognitive function using Mini-Mental State Examination (MMSE),Montreal Cognitive Assessment (MoCA),Wechsler Intelligence Scale and Wechsler Memory Scale.The patients were divided into cognitive normal group (n=91) and cognitive impairment group (n=109).One hundred twenty-six normal subjects were enrolled as control group (n=126).The levels of fasting plasma glucose (FPG),postprandial plasma glucose (2hPPG),glycosylated hemoglobin (HbAlc) and the prevalence of diabetes mellitus were compared among the groups.The effect of blood glucose level on the cognitive function of PD patients was analyzed by Binary Logistic Regression.Results The levels of FPG,HbAlc and the prevalence of diabetes mellitus [5.19 (0.72),5.7％ (0.5％),14％] were significantly higher than those in the normal control group [4.85(0.79),5.6％ (0.5％),6％] (P＜0.05).The levels of FPG in PD patients with cognitive impairment [5.21 (1.32)] was significantly higher than that in PD patients with cognitive normal group [4.81 (0.95)] (P＜0.05).Although 2hPPG and HbAlc increased slightly in PD patients with cognitive impairment,the difference did not reach an significant level (P＞0.05).Binary Logistic Regression analysis showed that FPG(OR:1.764;95％ CI:0.06-3.244;P=0.068) was not associated with the impaired cognitive function in PD patients.Conclusion The present study has not revealed an association between the incidence of cognitive impairment in patients with PD and plasma glucose level although high plasma glucose may be a high risk factor for PD patients.