There is growing demand for eco-friendly materials. Microcrystalline cellulose (MCC) and Soy Flour (SF) are of increasing interest due to its renewability, biodegradability economic value and mechanical properties. The primary objective of this work was to evaluate the processing and mechanical, rheological and thermal properties of a 10% weight loading of soy and MCC in different transparent polymers. MCC and soy flour (FI-1 fibers) were supplied by TensTech and Solvaria Specialties respectively. The three polymers used as a matrix were polypropylene (film grade: - Exxon 4721E1), polycarbonate (Lexan HP2), and amorphous polyamide (Trogamid CX7323). The melts were blended by single and twin screw extrusion, then injection molded into test specimens. Also, for the polypropylene reinforced SF and MCC, the effect of five weight percent of polypropylene grafted maleic anhydride (compatibilizer) was also investigated. Highly filled polymers exhibit altered viscoelastic behavior from neat resin, and so the relaxation spectrum can aid to understand dispersion in the composite. Accordingly, linear rheological properties of 10% filled Soy and MCC filled composites were studied using a rotational parallel plate rheometer. The elastic behavior of all the three filled polymer composites was examined through the examination of stress relaxation data and storage, loss modulus with frequency. The increase in storage modulus is attributed to increased polymer-filler interaction.