Polyester elastomers were prepared by block copolymerization of dimethyl terephthalate (DMT), butanediol (BDO), and polytetramethylene glycol (PTMG). Polyester from DMT and butanediol forms a high-melting hard segment in block copolyester to prevent undue chain slippage when fibers are stretched. High elongation was provided by soft segment which consisted of condensation product from DMT and PTMG.