PURPOSE: To curtail a working time and to obtain a high quality leather by adding a specified fluorochemical oligomer as a working auxiliary into an aqueous treatment composition working bath.

CONSTITUTION: In the production of leather from animal hide, at least 0.001 wt.% of an anionic, cationic, nonionic, or amphoteric fluorochemical working auxiliary having an aliphatic group containing at least 10 wt.% of fluorine and a water-soluble group is added into at least one aqueous treatment working bath in each process of water-immersion, recovery, pickling, degreasing, and tanning. The auxiliary is shown by the formula (Rf)QZ (Rf is a 3 or more C saturated, monovalent, non-aromatic fluoro-aliphatic group, Q is a linkage group or a covalent bond, Z is a water-soluble polar group, (n) is 1, 2) or a fluorochemical oligomer having a number of pendant fluoro-aliphatic groups Rf linked to a water-soluble poly(oxyalkylene) part.