Abstract: The expressions of aplipoprotein E (ApoE), tumor necrosis factor-α (TNF-α) in Alzheimer’s disease (AD) patients with different levels of estrogen were investigated to evaluate the diagnosis of combined PET/CT imaging (¹¹C-PIB and ¹⁸F-FDG) on AD. A total of 75 female AD patients were divided into low level of estradiol group (E₂<16.2 pmol/L, n=36) and normal level of estradiol group (16.2 pmol/L≤E₂<65.7 pmol/L, n=39) according to their estradiol levels. All the patients underwent PET/CT imaging (¹¹C-PIB and ¹⁸F-FDG). The sensitivity of PET/CT imaging, the standard uptake value radio, the expression rates of subtype ApoE (ε2, ε3, ε4), and the expression levels of TNF-α were detected. The relationship between E₂ and the expression rates of ApoE, the levels of TNF-α and SUVR were analyzed by Pearson analysis. In the low level of E₂ group, the sensitivity of PET/CT for ¹¹C-PIB alone, ¹¹C-PIB combined with ¹⁸F-FDG was higher than in normal E₂ group (χ²=4.869,P=0.027; χ²=3.636, P=0.047）; while the sensitivity of ¹⁸F-FDG PET/CT imagings on brain between the two groups had no significant difference (χ²=2.007, P=0.157). The expression level of E₂ with SUVR and the expression level of TNF-α in two groups of AD patients had the negative correlations (r=-0.363, P=0.001; r=-0.248,P=0.032). The expression rate of ApoE ε4 allelic genes of AD patients was higher than that of ε2 and ε3 allelic genes, and there was higher expression rates of ApoE in AD patients with the low E₂ group (Z=-2.228,P=0.026）. ¹¹C-PIB and ¹⁸F-FDG PET/CT had high value of diagnosis in AD patients.