To provide a method for preventing polymerization of styrenes, capable of preventing the polymerization for a long time not to speak of preventing the polymerization at its initial stage, and excellent in handleability, by considering their retention times in equipment for treating the styrenes or process fluids containing the same.

This method for preventing the polymerization of the styrenes comprises adding a combination of (A) piperidine-1-oxyls and (B) quinones of which the each has at least one hydroxyl group in its molecule to a process for producing, purifying, storing or transporting the styrenes.