Biomarker study on dementia has developed widely. In applying biomarkers, there seems to be several utilizations such as presymptomaticand early-stage detection, differential diagnosis, and evaluation of treatment effect. Currently, most reliable fluid markers are amyloid peptide (Aβ) with microtubule-associated protein tau (TAU) and phosphorylated TAU (P-TAU) detected in cerebrospinal fluid (CSF). Aβ42 correlates with plaque pathology, TAU reflects the intensity of neuroaxonal degeneration, and PTAU may correlate with neurofibrillary tangle (NFT) pathology. An attenuation of the level of Aβ42 and elevation in the ratio of Aβ42 relative to the shorter major species of Aβ42 peptide with 40 amino acid residues (Aβ40) has been identified as significant events in the early stage of Alzheimer’s disease (AD) pathology. In addition, there is great interest in blood-based markers of AD since blood extraction is much less invasive. Moreover, plasma biomarkers can be measured at relatively low expense once a standard system of measurement is established. Although there is not yet an establish‐ ed or validated diagnostic test for plasma biomarkers, there is great interest in bloodbased markers. We will summarize reported biomarkers, describe our novel potential plasma biomarker for AD (annexin A5), offering a strategy for selecting candidates, and show our results and evaluation.