A poly(3-hydroxybutyric acid) and wood flours (PHB/wood flours) composite and an acrylic acid-grafted PHB/wood flours composite were characterized and their properties were examined and compared. Mechanical properties of PHB became significantly worse when it was blended with wood flours, due to the poor compatibility between the two phases. Much better dispersion and homogeneity of wood flours in the polymer matrix was obtained when PHB-g-acrylic acid (AA) was used in place of PHB in the composite. Improved mechanical and thermal properties of the PHB-g-AA/wood flours composite, notably an increase in tensile strength at breakpoint, evidenced its superiority to the PHB/wood flours composite. Furthermore, PHB-g-AA/wood flours composites were more easily processed because of their lower melt viscosity. Under soil and enzymatic environments, weight loss data indicated that both composites were more biodegradable with higher wood flours content. A reduction in tensile strength at break after exposure to soil and enzymatic environments was also observed in both blends, especially at high wood flours content. (c) 2006 Wiley Periodicals, Inc.