The effect of the higher order structure on the degradation behavior of bacterial homo-poly(3-hydroxybutyrate) (PHB) melt spun fibers by a PHB depolymerase from Commamonas testosteroni was investigated. After the enzymatic degradation, fibrillar structure remained at the surface of the drawn and annealed fibers, while a spongy structure appeared in the as-spun fiber. Similar spongy structure to the degraded as-spun fiber was observed in the core part of some drawn and annealed fibers after the fibrillar surface disappeared. The mechanical properties deteriorated as enzymatic degradation proceeded. After the amorphous region was degraded, beta -form crystal, which seems to have less ordered structure, degraded in advance to the alpha -form crystal as revealed by WAXS measurements. However, these tendencies were less pronounced for the fiber annealed at high temperature under high tension. This result suggests that the beta -form crystal in the fiber annealed at high temperature under high tension would have more ordered crystalline structure, which withstands against the attack by the enzyme.