Objective To investigate the relationship between plasma level of homocysteine and mild cognitive impairment (MCI) in elderly patients with leukoaraiosis (LA). Methods A total of 110 elderly inpatients with confirmed LA hospitalized in our department from August 2011 to Jan 2013 were enrolled in this study. And another 40 sex- and age-matched individuals served as normal control. The LA patients were divided into the MCI group (LA+MCI group, n＝60) and non MCI group (LA group, n＝50), and were also divided into another 3 groups according to the plasma level of homocysteine: low level group (＜16μmol/L, n＝31), middle level group (16μmol/L≤Hcy＜30μmol/L, n＝45), and high level group (≥30μmol/L, n＝34). Mini-mental state examination (MMSE), Montreal cognitive assessment (MoCA) and the activities of daily living (ADL) were used to evaluate the cognitive function. Results In comparison to normal individuals, plasma level of homocysteine was higher in the LA patients with or without MCI (P＜0.01, for all). In all the LA patients, their score and fasting blood glucose was negatively correlated with the plasma level of homocysteine (P＜0.01, for all). Compared with the LA patients with lower homocysteine, those with middle and high levels had lower MoCA score (P＜0.05), and the patients of higher homocysteine had significantly lower score than those of middle level (P＜0.05). Conclusion LA patients accompanied with MCI have higher plasma level of homocysteine, and the higher the level is, the more severe MCI is.