It is an object of the present invention to provide a water-based composite resin composition which has an excellent long-term storage stability and which enables formation of a coating film having an excellent water resistance and solvent resistance. The present invention relates to a water-based composite resin composition and a coating agent; the water-based composite resin composition containing composite resin particles (A) and an aqueous medium (B), the composite resin particles (A) containing polyester resin (a1) particles having a sulfonate group and an epoxy resin (a2) of which some or all parts are encapsulated in the polyester resin (a1) particles, wherein a mass ratio [(a1)/(a2)] of the polyester resin (a1) to the epoxy resin (a2) in the composite resin particles (A) is in the range of 95/5 to 30/70.