An object of the present invention is to provide an aqueous coating composition capable of forming a coating film having a superior finishing appearance. The present invention provides an aqueous coating composition comprising a polyester resin containing a predetermined or greater amount of long chain, straight-chain dicarboxylic acid and/or straight-chain diols having a predetermined or greater carbon number and having hydroxy groups and acid values within predetermined ranges; a urethane-associated thickener having a hydrophobic group and/or a polyacrylicacid-based thickener having a hydrophobic group; a curing agent; and a hydrophobic solvent, wherein the contents of the thickener and the hydrophobic solvent are within a specific range based on the gross amount of the polyester resin and the curing agent. The present invention also provides a method for forming a multilayer coating film using the aqueous coating composition.