In order to use a steel bridge for a long period, attention must be paid to corrosion. Corrosion of steel bridges occurs in the presence of oxygen and water. Oxygen exists in the atmosphere, but there are various ways of water supply, and one of them is dew condensation. Dew condensation is a general water supply method in steel bridges, but there are few studies on dew condensation. Then, in this study, from the viewpoint of dew condensation which is one of corrosion factors of steel bridge, temperature and humidity of the object bridge and girder temperature were measured, and generation situation of dew condensation in the bridge was grasped. In addition, the simple evaluation of dew condensation environment of the object bridge was also carried out using the inverse distance weighting method.