Direct exposure or intake of engineered nanoparticles (ENPs) to the human body will trigger a series of complicated biological consequences. Especially, ENPs could either up- or downregulate peptide fibrillation, which is associated with various degenerative diseases like Alzheimer's and Parkinson's diseases. This work reports the effects of gold nanoparticles (AuNPs) with different shapes on the aggregation of an amyloid-beta peptide (A beta(1-40)) involved in Alzheimer's disease. Two kinds of AuNPs were investigated, i.e., gold nanospheres (AuNSs, similar to 20 nm in diameter) and gold nanocubes (AuNCs, similar to 20 nm in edge length). It was found that AuNPs play a catalytic role in peptide nucleation through interfacial adsorption of A beta(1-40). AuNSs with hybrid facets have higher affinity to A beta(1-40) because of the higher degree of surface atomic unsaturation than the {100}-faceted AuNCs. Therefore, AuNSs exert a more significant acceleration effect on the fibrillation process of A beta(1-40) than AuNCs. Besides, a shape-dependent secondary structure transformation of A beta(1-40) with different AuNPs was observed using Fourier transform infrared spectroscopy. The variation of peptide-NP and peptide- peptide interactions caused by the shape alteration of AuNPs influences the equilibrium of inter- and intramolecular hydrogen bonds, which is believed to be responsible for the shape-dependent secondary structure transformation. The study offers further understanding on the complicated NP-mediated A beta aggregation and also facilitates further development on designing and synthesizing task-specific AuNPs for amyloid disease diagnosis and therapy.