A process for the isolation of 4,4'-dichlorodiphenyl sulfone from a mixture of dichlorodiphenyl sulfones in which the ratios of the masses of 2,4'-dichlorodiphenyl sulfone and 3,4'-dichlorodiphenyl sulfone to the mass of 4,4'-dichlorodiphenyl sulfone are respectively from 0.5% to 20% and from 0.5% to 30% by treating the mixture with an alkanol at temperatures of from 20.degree. C. to 250.degree. C., cooling, and separating the pure 4,4'-dichlorodiphenyl sulfone that precipitates.