Abstract: The present disclosure provides an additive and a method for terminating polymerization and/or reducing viscosity of polymer solution. The additive comprises a carboxylic acid, an alcohol, a salt chosen from alkali metal salts, alkaline earth metal salts, ammonium salts, and any combination thereof, and optionally, water. The method of the present disclosure comprises adding the additive according to present disclosure into a polymer solution and mixing the resulting mixture. The additive of the present disclosure can terminate living polymer chain ends efficiently and can destroy catalytic active centers and can substantially reduce the viscosity of a polymer solution.