PURPOSE: To obtain a polyester which is excellent in flavor barrier properties, mechanical characteristics, and formability into film by inflation and gives a film excellent in heat sealability by replacing part of dicarboxylic acid units of polyethylene terephthalate with specific structural units.

CONSTITUTION: A polyester comprises glycol units consisting mainly of ethylene glycol units and dicarboxylic acid units consisting mainly of terephthalic acid units and including structural units of formulae I wherein n is an integer of 2-10 and II in such amts. that their sum is 5-30mol% based on the total amt. of the dicarboxylic acid units. The polyester has an intrinsic viscosity of 0.85dl/g or higher, an m.p. of 227°C or lower, and a melt flow rate at 230°C of 20g/10min or lower.