To explore apolipoprotein E gene variants distribution among the patients of Alzheimer's disease and vascular dementia for the elderly community population in Nanking, the polymerase chain reaction and restriction fragment length polymorphism techniques were employed to analyze the gene frequency of apolipoprotein E (ApoE) for 113 cases with Alzheimer's disease (AD), 85 cases with vascular dementia (VaD), 147 cases with questionable dementia (QD), and 396 dementia-free controls. It was found that ApoE ε4 gene container (37.17%) and allele frequency (21.24 ± 2.72) of ApoE ε4 in AD group were significantly higher than those in both control and VaD group (p < 0.05). With the increment of ε4 gene dose, the incidence of the AD was significantly increased. Compared with the control group, ApoE ε4 had risk ratio (RR) of 1.82 to develop AD (p = 4e-4), and attributable risk percentage (ARP) of 45%. These results suggest that ApoE ε4 gene may be responsible for up to 45% of the genetic component of Alzheimer's disease, and may act as a discriminator between AD and VaD as well.