Method for inhibiting polymerization of (meth)acrylic acid and esters thereof

Disclosed herein is a method for inhibiting polymerizable (meth)acryiic acid and esters thereof from polymerizing during their production, transportation and storage by using an inhibitor combination comprising an N-oxyl compound and at least one compound selected from the group consisting of manganese salt compounds, copper salt compounds, 2,2,6,6,-tetramethylpiperidine compounds and nitroso compounds. The N-oxyl compound is one or more kinds selected from 2,2,6,6,-tetramethylpiperidinooxyl, 4-hydroxy-2,2,6,6,-tetramethylpiperidinooxyl and 4, 4', 4''-tris-(2,2,6,6,-tetramethylpiperidinooxyl)phosphite. The combined use of the inhibitors provides superior inhibiting effect compared to the use of single inhibitors.