Objective To investigate the clinical value of miRNA-34a,miRNA-34c,and miRNA-135a in the early diagnosis of mild cognitive impairment (MCI) and Alzheimer's disease (AD).Methods The patients were collected in the outpatient and inpatient of Neurology during Aug 2014 to May 2016.The levels of miRNA-34a,miRNA-34c,an dmiRNA-135a were detected with quantitative real-time polymerase chain reaction (qRT-PCR).Results AD patients had higher level of miRNA-34a than the controls.The levels of miRNA-34c were higher in MCI and AD patients,while lower levels of miRNA-135a compared to the controls.Conclusions The miRNA 34a and miRNA-135a were likely to became the biomarker in early diagnosis of MCI and AD.