PURPOSE: To effectively separate adhering organisms without causing water pollution by applying, to the surface where the organisms grow, a separating agent comprising a specific heat-sensitive high-molecular compd. which is water- insol in the temp. range allowing the organisms to live and is water-sol. at a temp. lower than the above temp. range.

CONSTITUTION: An agent for separating adhering organisms (e. g. algae, barnacles, or shellfishes) comprises a heat-sensitive high-molecular compd. (e. g. poly-N-acryloylpiperidine) which is insol. in water or sea water in the temp. range allowing the organisms to live and insol. at a temp. lower than the above temp. range and which has an intrinsic viscosity [η[ at 27°C in tetrahydrofuran of 0.01-6.0dl/g. The agent in the form of film or soln. is stuck to or printed on a desired place of an object, dipped in water or sea water at the phase transition temp. of the agent or higher to allow the organisms to adhere, cooled to lower than the phase transition temp., and thus partly or wholy dissolved, thereby separating the organisms.