There is provided an antifouling coating composition capable of forming an antifouling coating film which has stable coating film consumption degree on ships, underwater structures and the like and which exhibits excellent antifouling property over a long term. The antifouling coating composition includes a hydrolyzable copolymer (A) and an antifouling agent (B), wherein the hydrolyzable copolymer (A) is, e.g., a metal salt bond-containing copolymer having a component unit derived from a monomer (a21) represented by the general formula (II): €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒCH 2 =C(R 2 )-COO-M-O-CO-C(R 2 )=CH 2 €ƒ€ƒ€ƒ€ƒ€ƒ(II) [In the formula (II), M is zinc or copper, and R 2 is a hydrogen atom or a methyl group], and a component unit derived from other unsaturated monomer (a22) copolymerizable with the monomer (a21), and wherein the antifouling agent (B) includes at least medetomidine.
