The effect of drawing and annealing on structure development and resulting properties of bacterial poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P(3HB-co-3HV)) fibers have been investigated. Melt spun and subsequently drawn and annealed fibers were characterized by wide-angle and small-angle X-ray scattering techniques. WAXS studies revealed that these fibers possess bimodal chain orientation with two populations of crystals: in the first population the chain axes are oriented primarily along the fiber axis and in the second population these chain axes are oriented in the transverse direction to the fiber axis. In the latter crystals, a- and b-axes are randomly distributed around their c-axes. At the annealing temperature of 100 degrees C, the relative population of the crystals oriented normal to the fiber axis was found to be large and their proportion decreases with the increase of annealing temperature. SAXS patterns were found to accompany the changes observed in the WAXS patterns. The tensile strength of these fibers improved by the increase of the proportion of the transversely or oriented chains.