Method of forming multilayer coating film including water-borne basecoat on automobile substrate

A method of forming a multilayer coating film composition comprising applying a water-borne base coating composition to an article to be coated, such as an automotive body, applying a clear coating composition thereon, and curing by heating, wherein the water-borne base coating composition comprises an emulsion resin obtained by emulsion polymerization of an α,β-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):