ObjectiveTo explore the Apolipoprotein-E （ApoE） gene polymorphism in patients with Alzheimer's disease （AD）, vascular dementia (VD) or mild cognitive impairment (MCI). MethodsPeripheral blood was taken from patient with AD, VD or MCI to determine the ApoE genotypes. ResultsThe most of the patients were ε3/ε3 genotype, while the ε2/ε2 and ε4/ε4 could not be detected. ε3/ε4 genotype （P=0.001） and ApoE ε4 allele （P=0.013） was more frequent in AD than in MCI. ApoE ε4 was more frequent in VD than in MCI （P=0.044）. ConclusionApoE ε4 allele is a risk factor in AD, and may be associated with VD and MCI.