Accumulation of amyloid fibrils is one of the likely key factors leading to the development of Alzheimer's disease and other amyloidosis associated diseases. Magnetic nanoparticles (NPs) have been developed as promising medical materials for many medical applications. In this study, we have explored the effects of Fe3O4 NPs on the fibrillogenesis process of insulin fibrils. When Fe3O4 NPs were co-incubated with insulin, Fe3O4 NPs had no effect on the structural transformation into amyloid-like fibrils but had higher affinity toward insulin fibrils. We demonstrated that the zeta potential of insulin fibrils and Fe3O4 NPs were both positive, suggesting the binding forces between Fe3O4 NPs and insulin fibrils were van der Waals forces but not surface charge. Moreover, a different amount of Fe3O4 NPs added had no effect on secondary structural changes of insulin fibrils. These results propose the potential use of Fe3O4 NPs as therapeutic agents against diseases related to protein aggregation or contrast agents for magnetic resonance imaging.