Aluminized steel sheets are promising materials for use as maintenance-free roofing or siding because of their superior corrosion resistance in comparison to galvanized steel sheets in a corrosive atmospheric environment. In this paper, the corrosion behavior of aluminized steel sheets has been investigated using test panels exposed for over 30 years. Corrosion of aluminized steel sheets was slight and their surfaces were covered with corrosion products mainly containing Fe. This Fe corrosion product seems to improve corrosion resistance by restraining the cathodic reaction. Corrosion products containing Fe seem to form minute α-FeOOH due to the effects of Al cations solved from the plating layer, preventing sources of corrosion like oxygen from diffusing into the plating layer.