PURPOSE: To provide a method for imparting the softness and bulkiness to wool fibers (regular wool) in a state of a yarn and obtain a softening and bulking treating agent therefor.

CONSTITUTION: This softening and bulking treating agent for wool fibers contains (A) a polyurethane prepared by reacting a polyol which is an N- substitution product of an alkylenediamine with a random or a block copolymer chain comprising 50-10wt.% propylene oxide with 50-90wt.% ethylene oxide with a di- or a polyisocyanate and (B) an aminosilicone at (50:50) to (90:10) weight ratio of the components (A):(B). Furthermore, the method for softening and bulking treatment comprises carrying out the oxidation treatment of the wool fibers with a mixture of a bromate with hydrogen peroxide, then adsorbing the softening and bulking treating agent on the resultant wool fibers and treating the wool fibers therewith.