Biobased plastics are making inroads into the marketplace. Poly(hydroxyalkanoates) (PHAs), such as the well known poly(3-hydroxybutyrate) (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerates) (PHBVs), are directly produced from bacterial fermentation using sugars or enzyme thinned cornstarch as feedstock. Besides polylactide, PHAs are another family of thermoplastic biopolymers that can be currently produced in large industrial scale. With the great effort made in the reduction of production cost, PHAs have attracted increasing interest in application development from both academia and industry. PHB and some PHBVs demonstrate high tensile strength and modulus comparable to many fossil oil based plastics, for example, polypropylene. Niche applications of biopolyesters, such as utensils, food packaging, grocery bags, and mulch films, are emerging. However, bioplastics including PHAs have only an insignificant share in the current marketplace dominated by fossil oil based plastics. While the effort is continuously being made to reduce resin costs, developing and manufacturing cost effective and performance enhanced products are critical to the promotion of bioproduct applications in the conventional plastics marketplace. In recent years, research has shown increasing interest in natural fiber reinforced biopolymer composites (biocomposites). In comparison with glass fiber, natural fibers have the advantage of low density, relatively high strength or modulus to weight ratio, low cost, good thermal and acoustic insulation, and ease of processing. In addition, extensive availability from various renewable resources makes natural fibers an economic and environmentally friendly alternative to glass fiber. In this study, we investigated the effects of several factors, including coupling agents and compatibilizer, wood flour (WF) particle sizes, talc, and processing methods, on mechanical and physical properties of PHA biocomposites. The polymers used were PHB and PHBVs containing 8 and 12 mol% of 3-hydroxyvalerate, namely PHBV8 and PHBV12. The coupling agents were titanate and zirconate (Lica, Kenrich Petrochemicals), and the compatibilizer was maleic anhydride (MA) grafted PHBV8 (MA-PHBV, containing 0.3% MA). Both extrusion and injection molding processes resulted in products with comparable mechanical properties, with injection molding yielding slightly higher flexural strength and modulus. The better performance of the products by injection molding might be attributed to higher orientation of WF and polymer molecules. Titanate and Zirconate coupling agents did not improve the compatibility of PHBV and WF. In fact, increasing the addition of these coupling agents resulted in continuous decrease in mechanical properties. This indicates that these coupling agents made the fiber surface more hydrophobic, which weakened the interfacial adhesion. MA-PHBV improved the compatibility between the PHBV and WF. WF with finer particle size also increased the strength of the composites but tended to decrease the modulus. Scanning electron microscopy (SEM) micrographs of fracture surfaces of the composites revealed that WF was well dispersed in the polymer matrix in most cases, irrespective of whether the surface was treated or not treated. Fiber pullout was identified in all composites, suggesting insufficient interfacial adhesion in the resulting composites. On the other hand, SEM indicated that the addition of MA-PHBV8 resulted in better wetting of the fiber surface as less fiber pullout was shown, comparing to the untreated fiber. Similarly, untreated fiber appeared to be better wetted than fiber treated with the titanate or zirconate coupling agents. These results are consistent with the mechanical testing. The effects of incorporating talc into the composites on the mechanical properties including morphology, creep resistance, and water resistance were also studied. Preliminary results from this experiment indicated that adding talc at certain levels could increase both the modulus and strength somewhat. At higher talc level, however, low flexural strength resulted.