PROBLEM TO BE SOLVED: To provide an antifoulant composition having the excellent antifouling property against underwater creatures.SOLUTION: There are provided: the antifoulant composition containing oxyalkylene group-containing organopolysiloxane represented by the following formula and copper and/or an inorganic copper compound； an antifouling coating thereof； an antifouling treated substrate in which a substrate is coated by the coating； and an antifouling method of the substrate.【課題】水中生物に対して優れた防汚性を有する防汚組成物を提供すること。【解決手段】下記式：で表されるオキシアルキレン基含有オルガノポリシロキサンと、銅および／または無機銅化合物を含有する防汚剤組成物、その防汚被膜、該被膜にて基材が被覆された防汚処理基材、並びに基材の防汚方法。【選択図】なし
