Surface diffusion during the decay of a two-dimensional nano-island formed on the Si(100) surface at 750 to 800K was studied using scanning tunneling microscopy and kinetic Monte Carlo simulation. From a surface diffusion point of view, decay proceeded so that the total diffusion rate of atoms on a surface decreased. Atoms at step edges moved more frequently than terrace atoms, which resulted in decay from the step edges of the island. In addition, a terrace atom took part in surface diffusion in the same way as did an atom from the steps of the island once it hopped up onto a terrace leaving a vacancy. The mass transport was not a specific atomistic process, but terrace atoms and vacancies on the terrace were involved. Repeated upward and downward hops of atoms and their difference were combined with surface diffusion, leading to mass transport. Tracking of atoms using simulation showed random walks with preferential diffusion along step edges, re-entering of the island, exchange of diffusing atoms and filling of a vacancy on the terrace. The motion of the center of the island to the upper side of the terrace, as observed by scanning tunneling microscopy, was well reproduced by the simulation. Surface Diffusion During Decay of Nano-Island on Si(100) at High Temperature. S.Toyoshima, T.Kawamura, S.Nishida, A.Ichimiya: Surface Science, 2004, 572[1], 84-92