Enzyme-catalyzed polycondensation for the synthesis of block copolymers was reported for the first time. Thermoplastic block copolyesters containing poly[(R)-3-hydroxybutyrate] (PHB) and poly[(R)-3-hydroxyoctanoate] (PHO) blocks were enzymatically prepared by one- or two-step lipase-catalyzed polycondensation. Novozym 435-catalyzed reaction of PHB-diol (M-n of 3100 g/mol, GPC), PHO-diol (M-n of 3200 g/mol, GPC), and divinyl adipate gave block poly(HB-co-HO) (M-n of 9800 g/mol, GPC) with randomly arranged blocks in 55% yield In two-step polycondensations, Novozym 435-catalyzed reaction of PHB-diol and divinyl adipate afforded 73% of PHB containing two vinyl ester end groups (M-n of 2700 g/mol, GPC), which was further reacted with PHO-diol in the presence of Novozym 435 to give block poly(HB-co-HO)s (M-n of 8800-14 200 g/mol, GPC) with A-B-type arranged blocks in 55-62% yield. The enzymatically prepared block copolyesters demonstrated T-m of 136-142 degrees C and 142-153 degrees C and T-g of -37 to -39 degrees C and were potentially useful thermoplastic biodegradable and biocompatible materials.