Solid anhydrous cosmetic composition, preparation process, cosmetic treatment processes and associated kit The present invention relates to a solid anhydrous cosmetic composition, in particle form, and comprising at least 30% by weight of anionic surfactants, at least 5% by weight of amphoteric surfactants, and at least 10% by weight of fillers. The invention also relates to a process for preparing this composition by granulation on a fluidized air bed and also to a process for the cosmetic treatment, in particular the care and/or the cleaning, of keratin materials, in particular the hair, comprising the application of said solid anhydrous cosmetic composition, alone or in combination with a hair conditioning composition. The invention also relates to a kit comprising said solid anhydrous cosmetic composition and said conditioning composition.