An antifouling coating composition having an excellent coating film strength and also has markedly superior antifouling properties, and a novel resin which is useful as a matrix resin for the composition are provided. The antifouling coating composition comprises a vinyl polymer (A) having, as a repeating unit, a structural unit (a) represented by the following formula (1): ##STR1##

(in the formula (1), X₁ and X₂ each independently represents an ester bond or a carbonyl group; R₁ represents an ethylene structure which forms a covalent bond with the carbonyl carbon atom and X₁ in the formula (1) at the same or adjacent carbon atom; R₂ represents a gem-alkylene group, a vic-alkylene group, an arylmethylidene group or an arylethylene group; and R₃ and R₄ represent an alkyl group or an aryl group, or a hydrocarbon group having a carbonyl group, an ether bond or an ester bond) and an antifouling agent (B).