In a process of producing isopropylnaphthols by oxidizing diisopropylnaphthalenes with molecular oxygen in a liquid phase to provide a reaction mixture which contains therein diisopropylnaphthalene monohydroperoxides and then acid decomposing the monohydroperoxides to isopropylnaphthols, the improvement comprising separating an organic layer from the reaction mixture, adding lower aliphatic alcohols of 1-4 carbons to the organic layer, crystallizing the diisopropylnaphthalenes while allowing the diisopropylnaphthalene monohydroperoxides to remain dissolved in the lower aliphatic alcohols, thereby to separate the monohydroperoxides from the diisopropylnaphthalenes.A further improvement in the process comprises crystallizing the isopropylnaphthols from aromatic hydrocarbons of 6-12 carbons.