Cellulosic materials were extracted from different agricultural wastes such as corn stalks, olive solid waste, and wood, by using a suitable extraction method. The extracted cellulosic materials were characterized using Fourier transform infrared spectroscopy. The produced cellulosic materials were used as reinforcements for low-density polyethylene to improve its tensile and thermal properties. A two-roll mill was used to mix the cellulosic materials (2.5–10 wt.%) with low-density polyethylene, and then the composite sheets were prepared by using a thermal press molding. The effects of filler type and its content on the mechanical and thermal properties were investigated by using the universal testing machine and differential scanning calorimeter, respectively. In general, with the increase of cellulosic materials content, there is an increase in the modulus of elasticity of the produced composites and a decrease of ductility. The ultimate tensile strength of the produced composites based on low-density polyethylene and cellulosic materials extracted from corn stalks and olive solid waste was found to be less than the tensile strength of low-density polyethylene, whereas the ultimate tensile strength of the composites based on low-density polyethylene and cellulose powder extracted from wood increased with increasing the cellulosic content. The addition of cellulosic materials was found to affect both the melting temperature of low-density polyethylene and its degree of crystallinity, depending on the cellulosic material source. © 2018, The Author(s) 2018.