PURPOSE: To prevent a natural polyamide-based fiber from yellowing by applying a treating liquid containing a specific compound to the fiber and then carrying out the dry heat treatment of the resultant fiber.

CONSTITUTION: This method for processing for preventing a natural polyamide- based fiber from yellowing is to apply a treating liquid containing a semicarbazide-based compound and a polyhydric alcohol-based epoxy compound to the natural polyamide-based fiber such as wool or silk by a dipping, a padding method, etc., and then carry out the dry heat treatment (at 50-110°C). Thereby, preventing effects on yellowing having practical durability are imparted thereto without deteriorating the feeling unique to the fiber. Furthermore, compounds of formulas I to IV can be exemplified as the semicarbazide-based compound and compounds of formulas V to VII can be exemplified as the polyhydric alcohol-based epoxy compound.