PURPOSE: To improve the stability of a vinylidene chloride resin to heat and light by a method wherein vitamin E, alkyl thiodipropionate and a phosphoric acid are added to the vinylidene chloride resin.

CONSTITUTION: 0.0005W0.2pts.wt. of vitamin E, 0.0005W0.2pts.wt. of 12W18C alkyl thiodipropionate and 0.0005W0.2pts.wt. of a phosphoric acid or a salt thereof are added to 100pts.wt. of vinylidene chloride copolymer. Example of vitamin E used is α,β,γ or δ-tocopherol or a mixture thereof. Examples of alkyl thiodipropionate are dilauryl thiodipropionate and distearyl thiodipropionate.