Objective To explore whether P300 can be the method for early diagnosis of vascular dementia.Methods 123 cases of multi infarct dementia(dementia group) were examined and compared with non dementia groups and healthy control groups according to 3 different age ranges respectively.Results There were significant differences between the dementia groups and the non dementia groups(P0.05) and between the non dementia and the healthy groups(P0.05).The latent period of P300 in patients over 60 years old of the dementia groups was longer than that in non dementia groups and the healthy controls.The latent period of P300 was prolonged by 1.5 S for every increase in one year of age.Conclusions The results suggest that the change in P300 can occur ealier than that in the intellective score of Haseyakawa Dementia Scales(HDS),P300 can be one of the methods for diagnosis of vascular dementia and favor early diagnosis and early treatment.Early treatment of vascular dementia with Ginaton is effective.