There was a correlation between BDNF and miR-211-5p( r=-0.805, P<0.001)in serum neurogenic exosomes( r=-0.805, P<0.001). BDNF was correlated with miR-211-5p in both the PD and control groups( r=-0.785 and-0.867, P=0.002 and 0.001). The miR-211-5p level was higher and the BDNF level was lower in the PD group than in the control group(0.30±0.08 vs. 0.17±0.04, 0.55±0.06 mg/L vs. 0.75±0.06 mg/L, t=7.125 and 6.368, P=0.000 and 0.000). The BDNF level was lower(0.45±0.07 mg/L vs.0.63±0.07 6.368 and 0.75±0.08 mg/L, t=8.999 and 7.608, P=0.000 and 0.000)and the MiR-211-5p level was higher(0.36±0.07 vs. 0.24±0.05 and 0.17±0.04, t=10.923 and 7.520, P=0.000 and 0.000)in the cognitive impairment group than in the non-cognitive impairment and control groups.The receiver-operating characteristics(ROC)curve showed that the area under the curve of miR-211-5p as a measure for cognitive impairment in Parkinson's disease was 0.860(95% CI 0.770-0.950)with a threshold of 0.32.The area under the curve of BDNF as a measure for cognitive impairment in Parkinson's disease was 0.891(95% CI 0.822-0.961)with a threshold of 0.67.BDNF seemed to be the target gene of miR-211-5p, since the latter could inhibit BDNF expression by reducing BDNFmRNA levels.