The present invention aims to provide methods to detect cognitive impairment including mild cognitive impairment and Alzheimer disease by using a protein or its partial peptide that differs in presence or absence, or in quantity between non-cognitive impairment and patients with cognitive impairment and further aims to present biomarkers comprising said protein and said partial peptide to be used to detect cognitive impairment including Alzheimer disease or mild cognitive impairment. Specifically, a biomarker for diagnosis of psychiatry disease or cognitive impairment comprising protein fragment or peptide of not less than 5 amino acid residues arising from at least one protein or peptide selected from the group of proteins consisting of amino acid sequence expressed by SEQ ID NOS: 1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, and 25 and selected from the group of partial peptide in these proteins consisting of amino acid sequence expressed by SEQ ID NOS: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, and 27. A
