Objective　To investigate the changes of serum α-synuclein and white matter structure in Parkinson’s disease patients with different status of cognitive impairment,and to explore the relationship between α-synuclein,changes of white matter structure and cognitive impairment in Parkinson’s disease.Methods 　Sixty patients with Parkinson’s disease were selected and divided into 3 groups according to their cognitive function:the normal cognitive group (PD-N),mild cognitive impairment group (PD-MCI) and dementia group (PDD).Patients with cognitive impairment were assessed with the MMSE and the MoCA.All cases were scanned with routine MRI sequence and diffusion tensor imaging (DTI) sequence.Fractional anisotropy (FA) were measured.The serum levels of α-synuclein were measured by ELISA.Results　The FA values of right temporal lobe,right cingulate posterior bundle,the genu of corpus callosum in PD-M CI group were lower than that in PD-N group (all P<0.05),the same findings were found regarding the FA values of left occipital lobe,left cingulate anterior bundle and the splenium of corpus callosum in the PDD group (all P<0.05).Analysis of logistic regression equation revealed that the genu of corpus callosum might be specific for the brain white matter;and so did left cingulate anterior bundle.The Spearman correlation analysis showed that there was a negative correlation between FA values of left frontal lobe and MoCA total score in PD patients,as well as right temporal lobe,left occipital lobe,left cingulate anterior bundle,right cingulate anterior bundle and the splenium of corpus callosum (all P<0.05),positively correlated between serum α-synuclein concentration and MoCA total score in PD patients (P<0.05).Conclusion　Diffusion tensor imaging might be valuable for the diagnosis of cognitive dysfunction in PD;and there might be a certain relationship between serum α-synuclein and cognitive impairment in Parkinson’s disease.