Abstract: The effect of two kinds of copolymer of vinyl chloride-vinyl acetate-vinyl alcohol, which are different in molecular weight, on the dispersibility of γ-Fe₂O₃ particles in butanone and on the adhesive tension between γ-Fe₂O₃ and the copolymer and on the peel strength between the copolymer and the polyester film are studied. The above-mentioned properties are improved when the molecular weight of the copolymer is 3.4×10⁴ as proved by both experiment and theory.