Preoriented poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (Nodax(TM)) films were obtained via the drawing of films to prestretching ratios ranging from 200 to 1000%. As expected, preorientation resulted in substantial improvements in the mechanical properties of the films from the corresponding increases in the amount and nature of the crystallinity present. Stress-strain curves in elongation showed a yield peak, which was relatively broad for the unoriented samples but became sharper, with a well-defined neck, as the extent of preorientation was increased. In addition, the preoriented films had higher modulus, toughness, yield stress, and tensile strength values. The attribution of these changes in the mechanical properties to changes in the crystallinity was supported by X-ray diffraction measurements. (C) 2004 Wiley Periodicals, inc.