The present invention is directed to an aqueous dispersion composition which comprises an ethylene-unsaturated carboxylic acid ionomer resin (A) neutralized with a mixture of ions including at least one divalent metal ion and at least one ammonium ion, (B) a non-water soluble vapor phase corrosion inhibitor, and (C) water. The dispersion exhibits good shelf-life and excellent rust-prevention properties. Durable corrosion resistant ionomeric coatings can be easily formed therefrom, which when applied to metal surfaces and baked, can form a rust-preventive coating layer showing excellent coating adhesion both to the metal surface and to an over coat paint. Such coatings are particularly useful when applied to a vehicle body or part thereof.