In this study cellulose nanowhiskers (CNW) were prepared by sulfuric acid hyrolysis from microcrystalline cellulose (MCC). The biopolymer composites of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV)/CNW, was fabricated by solution casting using N,N-dimethylformamide (DMF) as the solvent. Homogeneous dispersion of the whiskers was achieved and the composites exhibited improved tensile strength and modulus and increased glass transition temperature. The melt processing (extrusion and injection molding) of PHBV/CNW composites was also attempted. Despite using polyethylene glycol (PEG) as a compatibilizer, CNW agglomerates formed during freeze-drying could not be broken and well dispersed by the extrusion process due to the large surface area and the polar nature of CNW. As a result, the melt processed PHBV/CNW composites exhibited decreased strength and constant glass transition temperature, a typical trend of microparticle filled polymer systems. MCC was also treated by high-speed mechanical homogenizer to reduce its particle size down to nanoscale range. The homogenized MCC (HMCC) was blended with PHBV by melt processing with the same conditions. The obtained composites were found to have similar properties as the melt-processed PHBV/CNW composites due to poor HMCC dispersion. To the best of our knowledge, PHBV/ CNW system has not been studied so far. The treatment of MCC with high-speed homogenizer has also not been reported. This study augments the research on CNW nanocomposites.