Cosmetic compositions containing in a cosmetically acceptable medium, at least one fixing and/or conditioning polymer and at least one amphoteric polymer comprising from 1 to 20 mol % of at least one monomeric unit chosen from (meth)acrylate and (meth)acrylamide types having at least one fatty chain, the fatty chain having from 8 to 30 carbon atoms. This combination may provide markedly improved cosmetic properties (disentanglement, softness) compared with the properties obtained with either of the constituents used alone. These compositions are used for washing and/or conditioning keratinous materials such as the hair or the skin.