Abstract: The present invention provides a process for producing diphthaloyl peroxide comprising the steps of reacting particulate phthalic anhydride with aqueous hydrogen peroxide in a mobile slurry or paste and thereafter separating diphthaloyl peroxide from the aqueous phase. Preferably the minimum volume of hydrogen peroxide solution is employed commensurate with obtaining a mobile slurry or paste in a mole ratio of phthalic anhydride to hydrogen peroxide of 4:3 to 1:3. Preferably the reaction is effected at a temperature of from 25.degree. to 50.degree. C.Diphthaloyl peroxide is particularly suitable for washing/bleaching fabrics, optionally in conjection with an inorganic persalt e.g. sodium perborate, at a temperature of from 30.degree. to 60.degree. C.