To provide a polymerization inhibiting method of a copolymer comprising divinylbenzene and an aromatic vinyl compound permitting efficient inhibition of formation by polymerization of a copolymer comprising divinylbenzene, formed by the manufacture of the aromatic vinyl compound or intermixed as an accompaniment of manufacturing raw materials of the aromatic vinyl compound, and the aromatic vinyl compound over long hours in a distillation process, a purification process or a storage process of the aromatic vinyl compound, and permitting inhibition of stains by deposition of the formed copolymer on apparatuses or equipments.

2,6-Dinitrophenol compound (A) and a sulfonic acid compound (B) are simultaneously added in the manufacturing process, the purification process or the storage process of the aromatic vinyl compound. Preferably, (A) and (B) are used in a weight ratio of 99:1-50:50.