A coating varnish composition comprising (A) a polymer obtained by polymerizing one or more unsaturated carboxylic acids (a) with one or more unsaturated monomers (b), and (B) at least one additive selected from triazole derivatives, thiadiazole derivatives, and benzothiazole derivatives, and an antifouling coating composition comprising (i) said coating varnish and (ii) an antifouling agent containing a copper compound as a major component, do not show a danger of organotin copolymers, but provide a coating excellent in coating consuming properties and antifouling properties for a long period of time without causing gelation when mixed with a copper compound.