Background: Although plasma β-amyloid (Aβ) has been suggested to be a noninvasive diagnostic biomarker for Alzheimer’s disease (AD), its significance and validity have been inconclusive. Thus, it is quite important to establish a novel diagnostic method related to plasma Aβ. Methods: As our previous animal studies demonstrated a relation of glucose with plasma Aβ, we examined the effect of glucose loading on plasma Aβ levels in AD patients. After fasting, an oral glucose load was administered to AD patients and non-AD dementia patients, and subsequently, blood glucose, plasma insulin, and plasma Aβ levels were measured. Results: The plasma levels of baseline blood glucose, plasma insulin, and plasma Aβ were not different between the two groups. However, immediately after glucose loading, a significant increase in plasma Aβ40 and Aβ42 levels was observed in AD patients, whereas a mild decrease in plasma Aβ40 and Aβ42 levels was detected in non-AD dementia patients. Conclusion: The present study clearly demonstrated a different response in plasma Aβ40 and Aβ42 levels after glucose loading between AD and non-AD dementia patients, which is consistent with our previous animal studies. These findings suggest a novel diagnostic tool for AD using the elevation of plasma Aβ level after glucose loading, although further studies are necessary.