Disclosed is a method for assisting the detection of Alzheimer's disease or mild cognitive impairment, the method for assisting the highly accurate detection of Alzheimer's disease or mild cognitive impairment. In the method for assisting the detection of Alzheimer's disease or mild cognitive impairment, the amount of at least one miRNA selected from miR-122, miR-144, let-7f, miR-128-3p and miR-107 contained in a test sample separated from a living body is used as an indicator. A larger amount of miR-122 than that in a healthy individual, or a smaller amount of at least one miRNA selected from miR-144, let-7f, miR-128-3p and miR-107 than that in a healthy individual is indicative that the living body is more likely to have developed Alzheimer's disease or mild cognitive impairment.