2-O-Acetyl-20-hydroxyecdysone, an ecdysterones in insects and terrestrial plants, inhibits amyloid-β42 (Aβ42)-induced cytotoxicity. 2-O-Acetyl-20-hydroxyecdysone could decrease Aβ oligomer formation through promotion of fibrogenesis, transforming Aβ oligomers to the low-toxicity fibrils.