PURPOSE: To obtain the fiber excellent in the resistance to oxidative yellowing by adding a specific hindered phenolic compound and phosphorous acid to poly(hexamethylene adipamide).

CONSTITUTION: When poly(hexamethylene adipamide) is polymerized or extruded into fiber, 0.01 to 1wt.% of a hindered phenol selected from the compounds of formula I to III and 0.01 to 1wt.% of a phosphorous acid such as a phosphite ester or organic phoshite salt are added to give poly(hexamethylene adipamide) fibers having remarkability reduced yellowing properties on heating. Especially, the yellowing is reduced in the heat at on post-treatments to give the fiber with high whiteness, thus this polyamide fibers are suitably used in garments. An example of the hindered phenol is 2,4-bis(n-octylthio)-6-(4hydroxy-3,5-di-t- butylanilino)-1,3,5-triazine (formula I), and the phosphotous acid, is for example, tris(2,4-di-t-butylphenyl) phosphite.