Blends of bacterial poly(3-hydoroxyalkanoate) (PHA) with a medium-length side chain and polylactide (PLA), and blends of the chemically modified PHA (ePHA) with PLA, were prepared. The morphologies, some physical properties, and thermal behavior of the blends based on PLA were investigated by electron microscopies, testing machines, and a differential scanning calorimeter, respectively. A blend of uncrystallized rubbery second components, PHA and ePHA, produced an increase in the impact toughness of the PLA blends in contrast to a decrease in the tensile strength value. PHA, especially, with an inserted epoxy group side chain was more effective in improving the morphology and the physical properties than PHA. The ePHA particles existed in the PLA domain as a dispersed phase having a size of 0.1-1 mum. The results of the biodegradation test demonstrated that the PLA blends still maintained their biodegradability and were more accessible to hydrolysis and microbial attack, resulting in a greater weight loss than the pure PLA. (C) 2004 Wiley Periodicals, Inc.