Objective To investigate the clinical characteristics of cognitive impairment in the patients with asymptomatic unilateral severe internal carotid artery stenosis (ICAS). Methods A total of 80 patients with unilateral severe carotid stenosis (stenosis rate ≥70%)and 40 patients without carotid stenosis (control group)diagnosed by digital substract angiography (DSA)were analyzed retrospectively. According to the stenotic sides,the patients with severe ICAS were divided into a left stenosis group and a right stenosis group (n = 40 in each group). The North American Symptomatic Carotid Endarterectomy Trial (NASCET)criteria were used to grade the degree of stenosis. Montreal cognitive assessment (MoCA)was used to evaluate the cognitive function of the patients,and then the cognitive function of the patients in 3 groups was assessed. Results The MoCA total scores,visuospatial and executive functions,and language ability,and delayed memory scores of the patients in both left and right groups were lower than those of the control group. There were significant differences (21. 8 ± 3. 1,3. 4 ± 1. 3,1. 8 ± 0. 6,and 1. 6 ± 1. 3,respec-tively in the left stenosis group;22. 6 ± 2. 5,3. 5 ± 1. 1,1. 9 ± 0. 6,and 1. 7 ± 1. 4,respectively in the right stenosis group;and 26. 4 ± 1. 8,4. 2 ± 0. 9,2. 7 ± 0. 6,and 3. 8 ± 1. 0,respectively in the control group;all P < 0. 01). There were no significant differences in naming,attention,abstract ability,orientation ability scores compared with the control group (all P > 0. 05). There were no significant differences in the MoCA total scores and each single test score of the patients between the left stenosis and the right stenosis groups (P > 0. 05). Conclusion The patients with asymptomatic unilateral severe ICAS have cognitive impairment generally;it is characterized by delay memory,visuospatial and executive functions,and language dysfunction.