The human Islet amyloid polypeptide (20-29) (hIAPP(20-29)) is considered to be the core fibrillating fragment of hIAPP, which is associated with the pathogenesis of Type-II diabetes mellitus. A current challenge is the discovery of an efficient way to modulate amyloid aggregation and inhibit the toxicity of its aggregates. In this work, photoexcited porphyrins are successfully used to inhibit the fibrillation of hIAPP(20-29). Insights on the inhibitory mechanism are explored by the analysis of the secondary structure, the morphology and the mechanical properties of amyloid aggregates. In addition, photoexcited porphyrins displayed a retained inhibitory effect on hIAPP(20-29) aggregation without irradiation. These findings may establish a new avenue to inhibit the aggregation of amyloid peptide hIAPP and enrich the current selection of modulators. (C) 2017 Elsevier Inc. All rights reserved.