The scanning tunneling microscopy (STM) and the atomic force microscopy (AFM) have been applied to the direct study of the adsorption and aggregation of β-amyloid(1-42)(Aβ42) on the hydrophobic graphite surface. It was found that Aβ42 were preferentially adsorbed on graphite defects such as the edges. Aβ42 peptides self-assembled into intermediate protofibrils, which in turn self-associated to form fibrils. Usually, two or more fibrils intertwined to form the helical structure. These results will provide an important clue to studying the aggregation process of β-amyloid.