The title copolymer is obtained by reacting a dicarboxylic acid component mainly composed of terephthalic acid or its derivative with a glycol component composed of 0.5 mol % or more and less than 15 mol % of an aliphatic diol having 2 to 16 carbon atoms and more than 85 mol % and not more than 99.5 mol % of 1,4-cyclohexanedimethanol at least 80 mol % of which is in the trans form. This polyester copolymer has a high crystallization rate and an excellent heat resistance.
