PURPOSE: To obtain a new method for purification capable of preventing change of color from yellowish white to reddish brown, a fatal defect of polyiodoalkyl aryl sulfones and discoloration occurring by reaction with another component when used as a mildewproofing agent.

CONSTITUTION: This method of purification is carried out by dissolving a crude polyiodoalkyl aryl sulfone in an alcohol having ≤120°C boiling point under atmospheric pressure as a solvent, preferably dissolving iodine, p-toluenesulfonic acid and a monoiodoalkyl aryl sulfone in the solvent and recrystallizing the crude polyiodoalkyl aryl sulfone in the presence of these substances.