Abstract: Compositions including the dithiocarbamic acid derivative having ##STR1## group and at least one organo-tin compound selected from the group consisting of polymers having recurring units containing organo-tin, copolymers which are copolymerized with acryl compounds or vinyl compounds and organo-tin chemicals of ##STR2## are extremely effective for preventing the adhesion of marine organisms including marine microorganisms. This effect of the said composition is enlarged in the presence of copper compounds. R.sub.1, R.sub.2, and R.sub.3 represent an alkyl or phenyl, cycloalkyl group: Z; monovalent functional group containing sulphur or oxygen: and W; divalent functional group.