PURPOSE: To obtain a thermotropic arom. copolyester having an m.p. lower than that of a conventional one by subjecting four specific monomers to condensation.

CONSTITUTION: This copolyester comprises recurring units represented by formulas I, II, and III and, if necessary, recurring units represented by formula IV. In formulas II and III, Ar1 is an arom. and/or an alicyclic group; and Ar2 is an arom. group. Each arom. or alicyclic group in recurring units I to IV is optionally substd. The amts. of recurring units I, II, III, and IV are 2.5-60 mol.%, 2.5-45 mol.%, 2.5-45 mol.%, and 0-90 mol.%, respectively, based on the total amt. of recurring units, and the molar ratio of units II to units III is 0.95-1.05.