Nowadays, large quantities of lignocellulosic materials are produced in the world, such as coconut, sisal, jute and sugarcane bagasse fibers. The cellulose, the major component of natural fibers is a linear homopolymer of anhydroglucose and has a fibrillar structure and relatively high modulus of elasticity. To obtain cellulose from lignocellulosic materials, the separation of macromolecular components can be made by chemical, physical or enzymatic reactions. The process used in this work was essentially chemical. The alkaline pulping using NaOH/AQ (anthraquinone) preserved the quality of cellulose chains. These cellulosic fibers were inserted as reinforcement of expanded polystyrene (EPS). The EPS is a polymer extremely light and widely used as transportation packing. It is possible to reuse this polymer and apply as matrix in natural fiber composites. Before mixing fiber and EPS, this EPS is compressed by molding compression to decrease the polymer volume and then ground given a recycled PS. Finally, The fiber and recycled PS were blended in a single-screw extruder with the temperature profile at 140°C, 160°C and 180°C and then immediately twin-screw extruder with the temperature profile of 115°C, 150°C, 185°C, 185°C, 175°C, 175°C and 170°C. Then, the natural fiber composites was analyzed by thermal analysis (TGA – thermogravimetric analysis and DSC – differential scanning calorimetry) to studied the influence of processing on thermal properties, like thermal stability, temperature which this material could be processed, and the influence of the matrix fiber content in thermal events, as melting and degradation. The TGA curves showed that the composite has a thermal stability intermediate between the cellulose fiber and polymer matrix. DSC curves showed similar thermal events in respect to recycled PS. Acknowledgments to CNPq, Capes and UFRGS.