The present invention discloses an agent and a method of treating wool fibers using the agent which contains as an active ingredient, one or more water-soluble organic phosphine compounds selected from the group comprising hydroxyalkylphosphines expressed by the following formula: ##STR1## (wherein R.sup.1 denotes a hydroxyalkyl group having 1 to 10 carbon atoms and R.sup.2 and R.sup.3 each denotes an alkyl or hydroxyalkyl group having 1 to 10 carbon atoms) and derivatives thereof such as alkylene oxide addition products, phosphonium salts and quaternary phosphonium compounds thereof.