Oligomer formation of amyloid-β peptides (Aβ) is accelerated at a hydrophilic/hydrophobic interface. However, details of the acceleration mechanism have not been elucidated. In order to understand the eects of the interface on oligomerization at the atomic level, we performed molecular dynamics simulations for an A40 monomer in the presence and absence of the hydrophilic/hydrophobic interface. Nuclear magnetic resonance experiments of A40 peptides with gangliosidic micelles were also carried out. In the simulations and experiments, the hydrophobic residues of A40 bound to the interface stably. Moreover, we found that A40 formed a hairpin structure at the interface more readily than in bulk water. From these results, we discussed the acceleration mechanism of the oligomer formation at the interface.