To provide a method for suppressing the polymerization of a process fluid containing an aromatic vinyl compound in the production, purification, storage or transportation of the aromatic vinyl compound and provide a method for suppressing the polymerization of an aromatic vinyl compound by using an easily handleable compound having low toxicity and capable of suppressing the polymerization at initial stage and over a long period.

The method for suppressing the polymerization of an aromatic vinyl compound in the production, purification, storage or transportation of the aromatic vinyl compound comprises the use of (A) a 2,2,6,6-tetramethylpiperidin-1-oxyl compound, (B) 2-hydroxy-1,4-naphthoquinone and (C) an organic sulfonic acid compound at the same time.