Recently, the polymeric composites from renewable resources have attracted great interest. The trend to develop novel eco-friendly green materials from various renewable resources leads to the full or partial replacement of synthetic materials towards a sustainable world also. With a high modulus of elasticity, low density, low production cost and energy consumption, easy processability, renewable nature and recyclability, cellulose nano particles have attracted considerable attention as reinforcing filler in polymer matrix composites for exploring new applications. Polymethylmethacrylate (PMMA)/cellulose nanocomposite films were prepared by insitu polymerization with 10 weight% loading of cellulose nanofibers (CNF) and chemically modified cellulose nanofibers with maleic anhydride (M1CNF) and MMA (M2CNF) respectively to increase their interfacial compatibility with PMMA. The presence of the nanofiller increased the thermal stability of the nanocomposites, as measured by thermogravimetric analysis (TGA) and their glass transition temperature, measured by differential scanning calorimetry (DSC), as well as their average molecular weight measured by viscometric method. Mechanical test results showed that surface treatment of cellulose nanofibers significantly improved the tensile properties of PMMA nanocomposites. Biodegradation study was performed with soil burial method to analyze the effect of cellulose nanofibers on biodegradation. © (2013) Trans Tech Publications, Switzerland.