The present invention relates to a cosmetic composition for treating keratin fibres, preferably human keratin fibres such as the hair, comprising, in a cosmetically acceptable medium: —；one or more chemical oxidizing agents, —；one or more scleroglucan gums, —；one or more phosphorus-based sequestrants. The present invention also relates to a process for treating keratin fibres, preferably human keratin fibres such as the hair, comprising the application of the composition to the keratin fibres. The process according to the invention is preferably a process for bleaching, dyeing or permanently reshaping keratin fibres.
