The effect of the properties of a nanostructured gold surface (nano-Au surface) on the aggregation of Amyloid β(1-40) (Aβ40) was investigated. A nano-Au surface, in the form of immobilized nanoparticles, was prepared by using a thermal evaporator, resulting in the formation of nanosized clusters with sizes less than 10 nm. When Aβ40 was incubated with the nano-Au surface, abnormally large-sized tubular aggregates were formed on the surface and typical fibril formation was suppressed in the solution. This abnormally large tubular structure represents a novel type of Aβ40 aggregate. In the absence of the nano-Au surface, the diameters of the Aβ40 fibrils were less than 10 nm. However, the height of the tubular aggregates formed on a nano-Au surface was 80-100 nm. Such large-sized aggregates of Aβ40 have not been reported in previous studies dealing with interactions of suspended nanoparticles with proteins. This can be attributed to differences in the aggregation mechanism between immobilized and suspended nanoparticles. The formation of Aβ40 aggregates by nano-Au surface will provide the possible mechanism for abnormal fibril formation.