Abstract: The present invention relates to a composition for lightening keratin fibres, comprising, in a cosmetically acceptable medium:—at least 30% by weight, relative to the total weight of the composition, of one or more fatty substances free of carboxylic acid groups;—one or more peroxygenated salts;—one or more basifying agents; and—hydrogen peroxide; the peroxygenated salts/hydrogen peroxide weight ratio being greater than or equal to 0.2. This composition makes it possible to achieve equivalent, or even higher, lightening levels with markedly lower concentrations of peroxygenated salts and/or of hydrogen peroxide and/or milder pH conditions and/or shorter leave-on times. The composition then makes it possible to obtain advantages in terms of skin comfort and fibre protection. Under equivalent application conditions, this composition makes it possible to significantly improve the bleaching performance, in particular in terms of lightening power and efficacy, when compared with standard bleaching compositions.