According to the present invention, there is provided a process for inhibiting the polymerization of an aromatic vinyl compound which is capable of efficiently inhibiting the polymerization of an aromatic vinyl compound not only in an initial stage but also over a long term in the stage of producing, purifying, storing or transporting the aromatic vinyl compound, and which is excellent in handling. The present invention relates to a process for inhibiting the polymerization of an aromatic vinyl compound which requires the step of adding a 2-nitrophenol compound in combination with a sulfonic acid compound to the aromatic vinyl monomer during the stage of producing, purifying, storing or transporting the aromatic vinyl compound.