The present invention provides an antifouling paint composition comprising a hydrolyzable copolymer (A) and an antifouling agent (B), wherein (A) is at least one kind of hydrolyzable copolymer selected from the group consisting of (a1) a copolymer containing a bond of metal salt, which is an acrylic polymer or a polyester resin, and has a side chain terminal group represented by the formula (I): --COO-M-O--COR.sup.1 [where M represents zinc or copper and R.sup.1 represents an organic group]; (a2) a copolymer containing a bond of metal salt composed of a component unit (a21) represented by the formula (II): CH.sub.2.dbd.C(R.sup.2)--COO-M-O--CO--C(R.sup.2).dbd.CH.sub.2 [where M is the same as above and R.sup.2 represents H or CH.sub.3] and the other unsaturated monomer component unit (a22) which is copolymerizable with the monomer (II); and (a3) a silyl ester based copolymer composed of a component unit (a31) represented by the general formula (III): R.sup.7--CH.dbd.C(R.sup.3)--COO--SiR.sup.4R.sup.5R.sup.6 [where R.sup.3 is the same as R.sup.2, R.sup.4 to R.sup.6 represents a hydrocarbon group, R.sup.7 represents H or R.sup.8--O--CO-- (with the proviso that R.sup.8 represents an organic group or --SiR.sup.9R.sup.10R.sup.11 (R.sup.9 to R.sup.11 is a hydrocarbon group) and the other unsaturated monomer component unit (a32) which is copolymerizable with the monomer (III); and zinc sulfide is contained at an amount of 10 to 500 parts by weight with respect to 100 parts by weight of (A) as said antifouling agent (B) The antifouling paint composition according to the present invention gives less burden to the environment and exhibits excellent antifouling properties to algae.