An ester compound represented by formula (1) R.sup.1OOC--(CH.sub.2).sub.m--COOR.sup.2 (1) wherein R.sup.1 and R.sup.2 are different from each other and each represents a group of formula (2) --(R.sup.3O).sub.nR.sup.4 (2) wherein R.sup.3 is a C.sub.1-6 alkylene group; R.sup.4 is a C.sub.1-10 straight- or branched-chain alkyl group, a C.sub.6-12 aryl group, C.sub.7-15 arylalkyl group or a C.sub.7-15 alkylaryl group; m is an integer from 0 to 8, and n is an integer from 0 to 6.This compound is suitable as a plasticizer for biodegradable aliphatic polyester resins.