Aspects of thermal, morphological, and theological properties of biodegradable poly-D(-)(3-hydroxybutyrate) (PHB) blended with poly(ethylene oxide) (PEO) have been studied. Thermal properties and morphology of the blends were examined by scanning electron microscopy and differential scanning calorimetry, respectively. A rotational rheometer with parallel plate geometry was also adopted to investigate the theological properties of these blends. In addition, dynamic viscoelasticity was measured by a Rheovibron as functions of time and temperature. From these measurements, PHB and PEO were observed to be miscible in the melt state. In the case of the blend system 80/20 PHB/PEO by weight, the vacant domains of the PHB were filled with PEO particles, and this morphological state enhanced the theological properties. Furthermore, PHB and its blends were found to have high crystallinities, but to have unstable thermal behavior about T-m.