The invention relates to an ethylene cationic polymer comprising at least one primary, secondary or tertiary protonable amine function which is at least partially neutralized by a polymer organic acid neutralizing agent which contains at least one carboxylic, sulphonic and/or phosphonic acid function. Said invention also relates to a cosmetic or pharmaceutical composition comprising said neutralized polymer in a physiologically acceptable medium, in particular, cosmetically or pharmaceutically acceptable medium. A method for cosmetically treating keratinic materials, such as a body of face skin, nails, hairs, eyebrows and/or eyelashes, consisting in applying the inventive cosmetic composition to said keratinic materials is also disclosed.
