This study examines the properties of polyhydroxybutyrate (PHB) when blended with two types of maize starch Starch 1. (containing 70% amylose) and Starch 2 (containing 72% amylopectin). The PHB/starch blends were prepared by melt compounding at a ratio of 70/30 by weight and characterized in terms of their morphology, structure, thermal, rheological, and mechanical properties. The results show that starch granules act as a filler in PHB/starch blends and also act as a nucleating agent causing a very significant reduction in the size of the PHB spherulites. There were found to be significant improvements in thermal, rheological, and mechanical properties, and these were greater for blends containing Starch I than those containing Starch 2. These improvements are attributed to enhanced hydrogen bonding between PHB and Starch 1. with high-amylose content. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 116: 688-694, 2010