Abstract: An object of the present invention is to provide a modification method capable of affording animal hair having an anti-pilling property through simple treatment. The present invention provides a method for modifying animal hair, including a reduction treatment step of treating animal hair with a reduction treatment liquid containing a reducing agent under a neutral or weakly alkaline condition, and an enzyme treatment step of treating the animal hair subjected to the reduction treatment with an enzyme treatment liquid containing a water-soluble protein and a transglutaminase.