In a pathological mechanism of Alzheimer's disease (AD), amyloid β peptide (Aβ) 1-42 plays a crucial role. However, the detailed pathological mechanism remains unclear. This elucidation is hampered by handling difficulties of Aβ1-42 due to its poor water-solubility and uncontrollable aggregation. These properties prevent reproducing neurotoxicity-related assembly events of Aβ1-42 in the experiments, leading to discrepant study outcomes. Namely, such properties of Aβ1-42 are serious obstacles to establish an experiment system that clarifies the pathological mechanism of Aβ1-42 in AD. To solve these problems, we developed “click peptide” of Aβ1-42 based on the “Ο-acyl isopeptide method”. The click peptide, which contains an Ο-acyl instead of N-acyl residue at Gly²⁵-Ser²⁶ of Aβ1-42, is converted to Aβ1-42 via an Ο-to-N intramolecular acyl migration upon being triggered by pH-change (pH-click) or photo-irradiation (photo-click). The click peptide was 100-fold more water-soluble than Aβ1-42 and clearly adopted a monomeric random coil structure due to the Ο-acyl moiety in the peptide backbone. The click peptide was quickly converted to monomer Aβ1-42 with a random coil structure under physiological conditions upon an action (click). The obtained Aβ1-42 underwent both self-assembly and conformational changes with time. Because the in situ production of intact Aβ1-42 from the water-soluble and non-aggregative precursor could overcome the handling problems of Aβ1-42, this click peptide strategy would provide a reliable experiment system to investigate the pathological functions of Aβ1-42 in AD.