A water-borne base coating composition for automobiles which can give a coating film excellent in luster and in coloration comprises an emulsion resin obtained by emulsion polymerization of an ,-ethylenically unsaturated monomer mixture having an acid value of 3 to 50 and comprising at least 65% by mass of a (meth)acrylate ester whose ester moiety contains one or two carbon atoms, a coloring component comprising an optically coherent flaky pigment, and an acrylic polymer compound having a weight average molecular weight of 400,000 to 1,500,000 and represented by the general formula (1): ##STR1##