Abstract: A process for the filling of leather tanned with mineral, vegetable and/or synthetic tanning agents by treating the leather, in the acid pH-range , with an aqueous solution of a filling agent consisting of unsubstituted or substituted homo- or copolymeric acrylic acids and protein glue, alone or in admixture with further additives, as well as dry or liquid compositions thereof, are disclosed; thereby an even fullness of the leather is obtained without impairing the handle, the buffing properties, the tightness of the grain, the fine grain or the dyeability of said leathers.