Alzheimer's disease is very difficult to clinically diagnose. miRNAs constitute the promising next generation of Alzheimer's disease (AD) biomarkers and have the potential to diagnose neurodegenerative diseases. In this study, 94 subjects underwent extensive dementia screening. Let-7b miRNA was found to increase in association with the progression of AD, and the increase in let-7b miRNA was mainly due to CD4+ T cells in the cerebrospinal fluid (CSF). Additionally, let-7b was positively correlated with the expression of t-Tau and p-Tau. The inclusion of let-7b in A beta 40-A beta 42 or t-tau p-tau logistic regression and receiver operating characteristic predictive models can significantly improve the diagnostic performance. Overall, let-7b has an important association with the pathology of AD and can be used as an adjunct to improve the diagnostic performance of traditional AD biomarkers. (C) 2017 Elsevier Inc. All rights reserved.