To stabilize a polyamide, a polyester or a polyketone against degradation induced by oxidation, heat or light by using a composition prepared by adding a specified phosphite and a sterically hindered phenol to the polymer.
This composition comprises a polyamide, a polyester or a polyketone liable to degradation induced by oxidation, heat or light, a phosphite represented by formula I, and a compound represented by formula II (R1 is a 1-4C alkyl; n is an integer of 1-4; X is methylene or a group represented by formula III; Y is O or -NH-; when n=1, X is bonded to a group V, and Y is bonded to R2 (e.g. 2-12C alkylene); when n=3, X is bonded to methylene or a group of formula VI (the ethylene group is bonded to R2 (formula III)); and when n=4, X is bonded to a group represented by formula VIII, and Y is bonded to R2 (4-10C alkanetetrayl)).
