PURPOSE: To obtain the titled composition of low toxicity for application to underwater structures such as ships or pipelines to prevent their surfaces from attachment and growth of aquatic organisms, by incorporating a base resin with such specific ingredient(s) as N-(fluorodichloromethylthio)-phthalimide as antifouling agent.

CONSTITUTION: The objective composition can be obtained by incorporating (A) 100pts.wt. of a base resin (on a solid bases) with (B) as antifouling agent(s) of low toxicity, pref. 10W150pts.wt. of at least one sort of compound selected from N-(fluorodichloromethylthio)-phthalimide, N,N'-dimethyl-N'-phenyl-(N'-fluorodichloromethylthio)-sulfamide and benzimidazolylmethyl carbonate. Furthermore, this composition is preferably combined with ≤150pts.wt. of such general antifouling agent(s) as organotin compound, chlorinated organic compound, thiuram compound, or carbamate compound.