PURPOSE: To obtain a vinyl chloride resin composition having high safety and high stability to heat, by incorporating a dialkyl ester of an unsaturated aliphatic dicarboxylic acid into a vinyl chloride resin.

CONSTITUTION: 0.1W50pts.wt. dialkyl ester of an unsaturated aliphatic dicarboxylic acid of formula I [where R1 and R2 each are a 1W15C alkyl; R3 and R4 each are a group of formula II (where n is 0W6, usually 1 or 0), usually R3 and R4 each being H or one of R3 and R4 being a methyl and the other being H] (e.g. a dialkyl maleate or a dialkyl fumarate) and 0W200pts.wt. another plasticizer (e.g. a dialkyl phthalate or a dialkyl epoxyhexahydrophthalate) are incorporated into 100pts.wt. vinyl chloride resin.