In this study, the behavior of biocomposites reinforced with natural fibers from African palm and sugar cane in a recycled polyethylene matrix is investigated. The aim is to analyze the rheological and mechanical properties of these materials to optimize their processability by injection. Natural fibers treated through a steam explosion process and subsequent drying and grinding were used to obtain a size suitable for extrusion. Biocomposites with different percentages of fiber (30% and 40%) were prepared and evaluated by melt flow index (MFI) and capillary rheometry tests. The results indicated a significant reduction in material fluidity with increasing fiber content, which was mitigated by the addition of a lubricant additive, stearic acid. Simulation of the injection process made it possible to determine crucial parameters such as injection pressure and filling time. Subsequently, injection tests were carried out varying the temperature and fiber concentration, followed by tensile tests to evaluate the mechanical resistance of the injected specimens. The results showed that the addition of the additive significantly improved the fluidity of the material, facilitating its injection without damaging the machinery and maintaining good mechanical properties. This study provides a solid foundation for the development of biocomposites eco-friendly with potential applications in the plastics industry.