Cosmetic process for treating keratin fibres, comprising the application of a base composition and a composition comprising a polyol The present invention relates to a cosmetic process for treating keratin fibres, preferably human keratin fibres such as the hair, in particular for conditioning keratin fibres, using a combination of at least two different compositions, the first composition comprising one or more oxyalkylenated, preferably oxyethylenated, silicones, one or more cationic surfactants, and less than 10% by weight of water relative to the total weight of the composition, and the second composition comprising water and one or more polyols. The invention also relates to a kit comprising the two compositions. Finally, the invention relates to a ready-to-use cosmetic composition for treating keratin fibres.