Segmented block cololyetheresters based on poly(trimethylene terephthalate) and poly(teramethylene ether glycol) (3GT/PTMGT) were synthesized with various hard segment contents. The number average molecular weights of PTMG selected were 1000, 2000, and 2900. Copolymer composition was determined by $^{1}H$-NMR experiment. The effects of hard segment content and hard segment length on the thermal properties of copolytheresters were studied. 3GT/PTMGT showed higher melting temperature and higher crystallinity than 4GT/PTMGT of the same hard segment content.