The rapid development of electronic systems and telecommunications has resulted in a growing and intense interest in microwave electromagnetic absorber technology and microwave absorber materials. In this study, thermoplastic natural rubber barium ferrite composite was developed using micro and Nano barium ferrite filler. This paper presented the improvement of the mechanical properties of the thermoplastic natural rubber barium ferrite (TPNR-BF) composite when the size of barium ferrite filler changed from 3 um to 55 nm. TPNR was prepared as hosting material, and the barium ferrite with particle size 3 um was used as filler. Five samples of the composite were prepared with barium ferrite content range from 0% to 20% by an increment of 5%. The same procedure was used to prepare five samples using barium ferrite with a particle size of 55 nm. Physical and Mechanical properties of the composite were determined such as density, SEM, hardness, stiffness, tensile stress, and strain. Also, the magnetic properties and hysteresis diagram and SEM were evaluated for both composites barium ferrite types. The results indicate that all mechanical properties decline with the increasing BF content due to the increasing size of the weak interfacial zone between the polymer and the filler. This trend could be enhanced by replacing the micro barium ferrite with Nanosize barium ferrite. The level of improvement in mechanical properties increases at high filler content.