Abstract: A heat exchanger, e.g. that used in an air-conditioner, having a plurality of spaced plate-fins with narrow distance in parallel and a plurality of heat transfer pipes passing through said fins, said fins being coated with an aqueous coating composition comprising 100 parts by weight of a resin composition for water paint in solids content, 5 to 95 parts by weight of a surface active agent and 5 to 65 parts by weight of synthetic silica and baked at a temperature of 120.degree. C. to 200.degree. C. for 10 to 40 minutes to give a coating film of 3 to 20 .mu.m, has excellent hardness and corrosion resistance without damaging hydrophilic properties.