The objective of this work is to modify coconut shell powder (CSP) using various silane coupling agents and to study the effect of modification on the interfacial adhesion and mechanical properties of the fillers in the binary blend of thermoplastic polyurethane and natural rubber. Mechanical properties such as tensile strength, tear strength, hardness and abrasion resistance were evaluated. Results revealed that, compared to triethoxyvinylsilane modified CSP composites, glycidyloxypropyltrimethoxysilane treated CSP showed higher tensile strength and better interfacial adhesion with the matrix. The efficiency of the silane treatment is further characterized by the FT-IR analysis of fillers and the morphological study of both the CSP and the composites. FT-IR studies demonstrated that the silyl parts of both silane coupling agents efficiently grafted to the CSP. SEM images of treated CSPs provide ample evidence for the increased mechanical properties of the composites. The increased thermal stability of is evident from the thermo gravimetric analysis.