The objective of this study was to evaluate the influence of the wood fiber surface on the crystallization behavior of thermoplastic polymers. Unbleached and bleached kraft pulp fibers were used for this study with 100% polypropylene (PP), 95% PP/5% maleic anhydride Polypropylene (MAPP), and 100%. MAPP at 150 degrees C. Nuclei were induced at the ends of the fibers and on damaged surfaces while poor crystallization behavior was observed on the fiber Surfaces using 100%, PP. Enhanced MAPP induced transcrystallization on the wood fiber surfaces; the nucleation density also increased with the addition of MAPP. Oxygen/carbon (O/C) ratios of smooth surfaces, damaged surfaces, and the ends of wood fibers also indicated that the oxidation process of both wood fiber and thermoplastic polymer affected the crystallization process Without MAPP addition. It was observed that the MAPP played a role in increasing numbers Of nuclei on the linear fiber surface, to induce transcrystallization. Dynamic mechanical properties increased 52%, with 100%, MAPP compared to the use Of 100% PP. Therefore, the increased thickness of transcrystalline layer and nucleation density on the surface of wood fiber positively correlated with the dynamic mechanical properties of wood fiber-plastic composites. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1958-1966, 2010