A series of polyhydroxyalkanoate (PHA) copolymers consisting of short-chain-length (SCL) and medium-chain-length (MCL) 3-hydroxyalkanoate (3HA) monomers were synthesized in the recombinant Ralstonia eutropha PHB(-)4 harboring a low-substrate-specificity PHA synthase PhaC2(ps) from Pseudomonas stutzeri 1317. These polyesters, whose monomer compositions varied widely in chain length, were purified and characterized by acetone fractionation, nuclear magnetic resonance (NMR), gel-permeation chromatography (GPC), and differential scanning calorimetry (DSC). This was the first time that the physical properties of PHA copolymers polymerized by PhaC2(ps) were characterized. The results indicated that the variation in MCL 3HA contents did not have an obvious influence on the molecular weights of these PHA copolymers but was effective in changing their physical properties. The variation in the thermal property of PHA copolymers with 3-hydroxyoctanoate (3HO) content was also investigated in this study.