Background: Blood biomarkers that can be used for preclinical Alzheimer's disease (AD) diagnosis would enable trial enrollment at a time when the disease is potentially reversible. Here, we investigated plasma neuronal-derived extracellular vesicle (nEV) cargo in patients along the Alzheimer's continuum, focusing on cognitively normal controls (NCs) with high brain beta-amyloid (A beta) loads (A beta+). Methods: The study was based on the Sino Longitudinal Study on Cognitive Decline project. We enrolled 246 participants, including 156 NCs, 45 amnestic mild cognitive impairment (aMCI) patients, and 45 AD dementia (ADD) patients. Brain A beta loads were determined using positron emission tomography. NCs were classified into 84 A beta- NCs and 72 A beta+ NCs. Baseline plasma nEVs were isolated by immunoprecipitation with an anti-CD171 antibody. After verification, their cargos, including A beta, tau phosphorylated at threonine 181, and neurofilament light, were quantified using a single-molecule array. Concentrations of these cargos were compared among the groups, and their receiver operating characteristic (ROC) curves were constructed. A subset of participants underwent follow-up cognitive assessment and magnetic resonance imaging. The relationships of nEV cargo levels with amyloid deposition, longitudinal changes in cognition, and brain regional volume were explored using correlation analysis. Additionally, 458 subjects in the project had previously undergone plasma A beta quantification. Results: Only nEV A beta was included in the subsequent analysis. We focused on A beta(42) in the current study. After normalization of nEVs, the levels of A beta(42) were found to increase gradually across the cognitive continuum, with the lowest in the A beta- NC group, an increase in the A beta+ NC group, a further increase in the aMCI group, and the highest in the ADD group, contributing to their diagnoses (A beta- NCs vs. A beta+ NCs, area under the ROC curve values of 0.663; vs. aMCI, 0.857; vs. ADD, 0.957). Furthermore, nEV A beta(42) was significantly correlated with amyloid deposition, as well as longitudinal changes in cognition and entorhinal volume. There were no differences in plasma A beta levels among NCs, aMCI, and ADD individuals. Conclusions: Our findings suggest the potential use of plasma nEV A beta(42) levels in diagnosing AD-induced cognitive impairment and A beta+ NCs. This biomarker reflects cortical amyloid deposition and predicts cognitive decline and entorhinal atrophy.