The subject of the present invention is therefore a method for the lightening and/or lightening dyeing of keratin materials, which consists in treating the keratin fibers with at least: a) one direct emulsion (A) comprising one or more fatty substances free of carboxylic acid groups, one or more surfactants, an amount of water of greater than 5% by weight of the total weight of the emulsion, and one or more oxidizing agents; and b) one direct emulsion (B) comprising one or more fatty substances free of carboxylic acid groups, one or more surfactants, an amount of water of greater than 5% by weight of the total weight of the emulsion, and one or more alkaline agents; the concentration of fatty substances free of carboxylic acid groups being at least equal to 25% by weight of the total weight of the composition obtained after mixing the two direct emulsions (A) and (B). This process does not have the drawbacks caused by the presence of high contents of alkaline agents, and uses dyeing and/or bleaching compositions having improved lightening properties and that are stable over time, while at the same time remaining at least as effective in terms of the uniformity of the lightening, while at the same time preserving the quality of the keratin fiber.