Alkaline and silane treatments were applied to wood flour (WF) to enrich its adhesion to bio-based thermoplastic polyurethane (TPU) matrix. TPU/WF eco-composites were prepared at a constant ratio of 30% by the melt blending process. The mechanical, thermo-mechanical, melt-flow, water uptake and morphological properties of the materials were investigated. Silane-treated WF filled composite exhibited better mechanical performance with respect to untreated WF due to enhancement of adhesion between WF and TPU matrix after surface treatments. This sample also gave the lowest water absorption value among composites. The results confirmed that silane treatment of WF led to significant improvement on the mechanical and physical properties of TPU-based composites in addition to an improved water resistance for outdoor applications.