<;P>;PROBLEM TO BE SOLVED: To provide an antifouling agent having an antibacterial activity against a wide variety of bacteria, also having an attachment-repelling activity against algae and aquatic organisms, having high solubility to organic solvents, thereby excellent in compatibility to resins and having high safety. <;P>;SOLUTION: This antifouling composition is constituted by using a silicone-modified antibacterial polymer consisting of an amino group-containing antibacterial polymer introduced with a polyorganosiloxane group, as an active ingredient. <;P>;COPYRIGHT: (C)2007,JPO&INPIT