β-Sheet Breaker Peptide iAβ5 is a potent degrader of cerebral amyloid-beta (Abeta). Abeta deposition is associatied with the Alzheimer disease (AD), due to its related toxicity linked to its beta-sheet conformation and/or aggregation. β-Sheet Breaker Peptide iAβ5 reproducibly induces in vivo disassembly of fibrillar amyloid deposits. Thus, β-Sheet Breaker Peptide iAβ5 prevents and/or reverses neuronal shrinkage caused by Abeta, and reduces the extent of interleukin-1beta positive microglia-like cells that surround the Abeta deposits. β-Sheet Breaker Peptide iAβ5 reduces the size and/or number of cerebral amyloid plaques in AD. β-Sheet Breaker Peptide iAβ5 labeled by hydrophobic benzyl alcohol (HBA) tag, can be used for quantitative assay by showing vivid blue color under acidic conditions.