An anti-fouling condensation curing organopolysiloxane composition is provided comprising in admixture, (A) 100 parts by weight of a base polymer in the form of a diorganopolysiloxane having at least two silicon atom-bonded hydroxyl or hydrolyzable groups in a molecule, at least 2 mol % of entire substituent groups being phenyl groups, (B) 0.5 to 30 parts by weight of a silane having at least two hydrolyzable groups or a partial hydrolytic condensate thereof, and (C) 5 to 100 parts by weight of a non-reactive dialkylpolysiloxane. The composition cures at room temperature to form a coating which is non-toxic, non-detrimental to the environment, and effective for preventing aquatic organisms from depositing and growing thereon over a long term.