Abstract: A substituted acylaminopolyorganosiloxane (A) is a polyorganosiloxane containing substituted acylamino groups linked to silicon atoms of the polysiloxane skeleton via alkylene bridges or mono- or oligo-[alkylene-amino or alkylene-(substituted acyl)amino]-alkylene bridges. The alkylene contains 2-4 carbon atoms and the substituted acylamino groups are at least in part of formula and for the remaining part are selected from substituted acylamino groups of the formulae in which: X1 signifies hydrogen or the group —SO3?M+, X2 signifies hydrogen or the group —SO3?M+, with the proviso that one of X1 and X2 is —SO3?M+ and the other is hydrogen, R signifies C2-6-alkylene or cyclohexylene, and M+ signifies an alkali metal or ammonium cation. The substituted acylaminopolyorganosiloxane (A) and compositions thereof, in the presence of non-ionic or/and anionic surfactants (B), can be used as fat liquoring agents for fat-liquoring of animal hides, skins or pelts.