〔Abstract〕 Objective To explore the changes of cognitive function before and after endovascular treatment of middle cerebral artery stenosis and its possible mechanism. Methods Twenty-two patients with middle cerebral artery stenosis were grouped into the treatment group and control group according to whether they received endovascular treatment or not. All subjects were evaluated at 3 d before operation, 3 d after operation and 3 months after operation.The changes of cognitive function between the two groups were compared. The cognitive function and emotion of patients were evaluated by Mini Mental State scale(MMSE), Montreal Cognitive Assessment scale(MoCA), Cambridge Geriatric Cognitive examination scale(CAMCOG-C), language fluency test, Wechsler visual replication,digit span test and neuropsychological scales,such as Hamilton Anxiety Scale( HAMA) and Hamilton Depression Scale( HAMD). Vascular stenosis,cerebral perfusion and collateral circulation were evaluated by CT angiography( CTA),CT perfusion imaging( CTP) and digital subtraction angiography( DSA). Results In the treatment group,the delayed memory in MoCA and the C1 of Wechsler visual replication were significantly improved during the 3-month follow-up period,and the score during the follow-up period was higher than that in the control group. While there was no significant difference in the abstract comparison of MoCA subitems between the treatment group and the control group,the abstract score in the treatment group was significantly higher than that in the control group during the follow-up period. The digital span sequence score of treatment group were significantly improved at 3 days after operation and 3-month follow up compared to that before operation. The collateral circulation in the treatment group measured by Multiphase( mC TA) and DSA was significantly improved after operation. In addition,the cerebral perfusion in the treatment group was significantly increased after operation,and the average transit time( MTT) was significantly decreased( P<0. 05). Conclusion Endovascular treatment of middle cerebral artery stenosis may improve the cognitive function of patients by improving collateral circulation and increasing blood perfusion.