Polyhydroxyalkanoates are a class of biodegradable polymers that may be used more as environmentally friendly materials if their mechanical properties can be improved. We approached this goal by modifying poly(3-hydroxybutyrate-co-3-hydroxyvalerate) with a well-established processing technique involving crosslinking the polymer chains and then drying a swollen gel of the network under uniaxial strain. The mechanical properties of the resulting oriented films were determined in continuous extension as a function of the degree of crosslinking and the extent of strain during the drying process. Crosslinking invariably improved the toughness. Similarly, the subsequent orientation of the process generally increased the toughness as well, but in some cases, a reduction in the extensibility, offset the increase in the ultimate stress at break and yielded reduced values of the toughness. (C) 2005 Wiley Periodicals, Inc.