A coated steel sheet coated with a composite coat, wherein said composite coat is a coat formed by compounding ethylene-unsaturated carboxylic acid copolymerization resin particles (A) having an average particle diameter of 20 to 100 nm and a silanol group and/or an alkoxysilyl group, silicon oxide particles (B) having an average particle diameter of 5 to 50 nm and an organic titanium compound (C), and wherein an amount of a coat of said composite coat is 0.5 to 3 g/m2.