Novel block copolyester containing biocompatible and biodegradable biopolyester blocks was prepared by polycondensation of telechelic hydroxylated Poly [(R)-3 -hydroxyoctanoate] (PHO-diol) and telechelic hydroxylated poly[(R)-3-hydroxybutyratel (PHB-diol) with terephthaloyl chloride (TeCl). Reaction of PHO-diol (M-p of 2100), PHB-diol (M-p of 3200), and TeCl at a ratio of 1.3:1:2.1 gave the block co-polyester PHOHBTe in 86% yield with a molecular weight M-p of 7200 (GPC). The chemical structure of the copolyester was confirmed by H-1-, C-13-, and COSY-NMR and IR spectra. On average, 2 PHO-diol, 1 PHB-diol, and 2 TeCl were incorporated in each molecule of the block copolyester PHOHBTe. For comparison, polyester PHOTe with a M-p of 7100 (GPC) was prepared in 81% yield by reaction of PHO-diol and terephthaloyl chloride at a molar ratio of 1:1.2. NMR analysis suggested that PHOTe contains 3 PHO and 3 Te units on average. While PHOTe containing no PHB block is soft-sticky, PHOHBTe containing both soft PHO and hard PHB blocks showed good thermoplastic properties with T-g of 129 and 140 degreesC and a T-g of -41 degreesC. Thus, for the first time, block copolyester containing PHO and PHB blocks has been prepared and demonstrated to be thermoplastic.