Ethylene propylene diene monomer (EPDM) bio-composites filled with silane-modified wood fiber (Si-WF) were fabricated by melt batch mixing and compression molding. The effects of fiber loading, silane modification, and in situ cross-linking on the water absorption, thermal, and mechanical properties were investigated. Due to the reduced surface energy of the modified wood fibers, the EPDM bio-composites with Si-WF showed substantially lower water absorption and higher thermal stability than EPDM with unmodified wood fibers. With Si-WF and in situ cross-linking, the tensile strength and modulus of EPDM bio-composites exhibited up to 115.3 % and 258.9 % improvement over the pure EPDM, respectively. This was because of the enhanced dispersion of the Si-WF in the elastomer matrix, as noted from the fractography study.