Provided herein is a cosmetic composition for washing and conditioning keratin fibers, comprising, in a cosmetically acceptable medium: (i) at least one organosilicon compound chosen from silanes comprising one silicon atom and siloxanes comprising two or three silicon atoms, wherein the at least one organosilicon compound also comprises at least one basic chemical functional group and at least one group chosen from hydroxyl and hydrolysable groups per molecule; (ii) at least one anionic surfactant chosen from sulfate and sulfonate anionic surfactants; (iii) at least one carboxylic anionic surfactant other than the at least one anionic surfactant of (ii) chosen from alkyl ether carboxylic acids and salts thereof, and (iv) at least one amphoteric surfactant. Also provided is a cosmetic process for treating keratin fibers, comprising applying the cosmetic composition to the keratin fibers.