The present invention provides a coating composition capable of forming a coating film having good performances such as an adhesive property even if coated on a deteriorated coating film surface of a high rust-preventive coating film of a tar epoxy resin coating material and the like without providing pre-treatment, and a coating method thereof. The above coating composition is a coating composition of an organic solvent type or solventless type comprising an epoxy resin having at least one epoxy group in a molecule and an amine base curing agent as resin components, wherein moisture of 1 to 30 parts by weight per 100 parts by weight of the solid matter of the coating composition is contained.