The present invention provides an inorganic-organic composite-treated zinc-plated steel sheet whose treated coatings do not contain any chromium and which is excellent in corrosion resistance after degreasing, coating adhesion and electrodeposition coating performance. The inorganic-organic composite-treated zinc-plated steel sheet, which is obtained by forming a zinc phosphate coating, in a coating weight of 0.3 to 5 g/m2, on the zinc-plated steel sheet surface and forming thereon a post-treatment coating, in a coating weight of 0.01 to 1 g/m2, by using a post-treatment composition containing at least one compound (A) selected from the group consisting of thiocarbonyl group-containing compounds, sulfide group-containing compounds and guanidyl group-containing compounds, an organic resin (B), a crosslinking agent (C) and an inorganic corrosion inhibitor (D).