Objective To investigate the correlation between plasma β-amyloid protein (Aβ) and its deposition on ¹¹C-PiB PET/CT.Methods A total of 69 elderly individuals were enrolled in the study from General Hospital of Shenyang Military Command, either with Alzheimer′s disease (AD) or with mild cognitive impairment (MCI) or with no dementia (normal controls,NC). All subjects underwent amyloid imaging with ¹¹C-PIB PET/CT and measurement of plasma Aβ42 and Aβ40. Five regions of interest (frontal, lateral temporal, parietal cortex, posterior cingulate/precuneus and anterior cingulate) were identified. The maximum standardized uptake value (SUVmax) was measured for the whole brain and each region of interest, and their correlations with plasma Aβ42 and Aβ40 were analyzed. SPSS statistics 18.0 was used for data analysis. Results Standardized uptake value ratio (SUVR) of Aβ42/Aβ40 decreased gradually in NC, MCI and AD groups, and ¹¹C-PIB SUVR increased gradually, with significant differences(P＜0.05). ¹¹C-PIB SUVR correlated negatively with plasma Aβ42 (r=-0.461) and Aβ42/Aβ40 (r=-0.633) ratio and positively with plasma Aβ40 (r=0.430), the difference being statistically significant (P<0.05). ¹¹C-PIB SUVR of brain regions increased gradually in three groups. Regression analysis showed that ¹¹C-PIB SUVR of frontal lobe, temporal lobe and precuneus could be predicted by plasma Aβ42/Aβ40 ratio with statistically significant difference (P<0.05), but ¹¹C-PIB SUVR and plasma Aβ42/Aβ40 ratio were of no statistical significance in the parietal lobe and posterior cingulate (P＞0.05). Conclusion The plasma Aβ42/Aβ40 ratio is able to predict brain amyloid deposition, and amyloid deposition on ¹¹C-PiB PET and plasma Aβ42/Aβ40 ratios have significant clinical potential as biomarkers.