A catalytic transesterification reaction on phenolic hydroxyl groups by a carboxylate-type ionic liquid, 1-ethyl-3-methylimidazolium p-anisate ([Emim][OAn]), was investigated using a model reaction with phenol and vinyl propionate. Undesirable contamination of the ester group formed on the phenol with an acyl group derived from the acyl anion in the [Emim] [OAn] was effectively suppressed. This catalytic reaction was applied to Kraft lignin, and the desired esterification was successfully promoted on the hydroxyl groups with a conversion of up to 94 mol %.