A new copolyester of 3-hydroxybutyrate (3HB) and 3-hydroxypropionate (3HP) was produced byAlcaligenes eutrophusin a nitrogen-free culture solution of 3-hydroxypropionic acid, 1,5-pentanediol, or 1,7-heptanediol. The copolymer composition varied from 0 to 7 mol% 3HP, depending on the type of carbon substrates supplied. Te bacterial copolyesters were characterized by1H and13C NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC). The copolymers were shown to have a random sequence distribution of 3HB and 3HP units by analysis of the 125-MHz13C NMR spectra. The melting temperatures (Tm) decreased from 178 °C to 150 °C as the 3HP fraction increased up to 7 mol%. It has been found that the presence of 3HP units in polyesters accelerates the rate of enzymatic degradation.