A composition for treating keratinous materials, particularly human hair, is disclosed, The composition is packaged in an aerosol device and forms a lacquer at the outlet of the device. Said composition contains (a) at least one silicone graft polymer including a polysiloxane portion and a portion consisting of a non-silicone organic chain, where one of said portions forms the main polymeric chain while the other is grafted onto said main chain; (b) at least 30 wt % of water, (c) at least one propellant; and (d) an organic solvent in an amount of 0-25 wt %; the above percentages by weight being based on the total weight of the composition in the aerosol. Such aqueous lacquers are useful for fixing and/or styling and/or conditioning hair.