This research aimed to clarify the corrosion condition of the main cables used for over 50 years on an actual suspension bridge. The cables were disassembled into the galvanized steel wires and the corrosion condition of them was assessed by two methods: the corrosion evaluation criteria based on the exterior appearance; the rust composition analysis. As an evaluation result by the criteria, the corrosion condition was the more outside, the more corroded, and the wires around the centre of the cables were not corroded. In addition, from the relations with the exterior appearance and the rust composition, this study proposed new corrosion evaluation criteria. According to the evaluation results by the proposed corrosion evaluation criteria, the condition which includes zinc corrosion and steel corrosion was assessed accurately.