The present invention relates to a composition for treating keratin materials, in particular keratin fibres, and in particular human keratin fibres such as the hair, comprising, in a cosmetically acceptable medium: at least one fatty substance in a content of greater than or equal to 10% by weight relative to the total weight of the composition, at least one oxyalkylenated (OA), preferably oxyethylenated (OE), nonionic surfactant comprising a number of OA units, preferably OE units, ranging from 1 to 9, at least one oxyalkylenated (OA), preferably oxyethylenated (OE), nonionic surfactant comprising at least 10 OA units, preferably OE units, the weight ratio of the amount of oxyalkylenated (OA), preferably oxyethylenated, nonionic surfactant(s) comprising a number of OA units, preferably OE units, ranging from 1 to 9 to the amount of oxyalkylenated (OA), preferably oxyethylenated, nonionic surfactants comprising at least 10 OA units, preferably OE units, being greater than 1, at least one chemical oxidizing agent, preferably hydrogen peroxide. The composition in accordance with the invention may be used for dyeing, bleaching or permanently reshaping keratin materials, in particular keratin fibres. It produces ready-to-use compositions that give good dyeing, bleaching or permanent-reshaping properties without degrading the keratin materials, in particular keratin fibres, and without impairing their cosmetic properties.
