The present invention provides a process for producing a mixture of dihydroxydiphenylsulfone isomers containing 2,4-dihydroxydiphenylsulfone, the process comprising heating 4,4-dihydroxydiphenylsulfone or a mixture of dihydroxydiphenylsulfone isomers containing at least 85 wt. % of 4,4-dihydroxydiphenylsulfone in the presence of phenol and sulfuric or sulfonic acid.