To prepare the subject safe repellent having preventing effects on the attachment of underwater attached organisms for a long period without any environmental pollution by including a microcapsule enclosing an alkali isothiocyanate and a binder ingredient therein.

This repellent for underwater attached organisms comprises (A) a microcapsule containing a core part formed of a gel-like polyurethane resin containing allyl isothiocyanate and a shell part, covering the core part and formed of a polyurea resin and (B) at least one of a water-soluble polyurethane resin and an aqueous emulsion of a synthetic resin as a binder ingredient. Thereby, the repellent excellent in antifouling properties and residual effects is obtained. An antifouling coating material comprising the ingredients A and B in a conventional coating material ingredient can be used in a form such as a coating on a part, etc., to be an object of preventing the attachment of underwater attached organisms.