After this, beridges to be constructed in port area, will enlarge in scale and number. So study on durability of bridges by the sea, must be done immediately to improve technique of maintenance for those bridges.
　I made a suvey on deterioration about bridges constructed by the sea under the control of Ministry of Transport all over the country, and analyzed it.then I got hold of the situation of deterioration about 106 bridges made of steel and 257 made of concrete.
　I investigated durability of steel-made bridges mainly about the questionnaire in the firt part of this paper. And in the second, I made a proposal of painting specification and standard of paints which are suitable for steel-made bridges by the sea.
　And in the last, I studied a possibility about application of weather-proof steel to bridges by the sea.