Until recently, synthetic filler materials have been the preferred choice for reinforcement of polymers to improve its toughness. However, natural filler and fiber materials are emerging as suitable alternatives to synthetic materials for reinforcing polymers due to their environmental friendliness, high abundance, renewability, and cost-effectiveness. In the present study, the waste portion of the fruit Citrus Maxima (CM) commonly known as Pomelo, in the form of fine powder was blended with Low-Density Polyethylene (LDPE) for making the composite using the injection molding method. The peel of CM consists of a foamy portion which was separated, thoroughly dried at 50–70 °C and ground into a fine powder and was used as an eco-friendly particulate filler with the LDPE matrix in different proportions (0, 5, 10, 15, and 20 wt%) in treated and untreated form. The filler was treated with 2 wt% of Silane coupling agent. XRD and FTIR confirmed the cellulosic behavior of the CM foam. The effect of filler content on the mechanical properties of the untreated and treated composites was investigated. The morphology and the microstructure of the composites were observed by XRD, FTIR, and SEM. The surface treatment showed significant improvement in the tensile strength, % elongation and impact strength for the treated composite at higher loading of filler. The mechanical behaviour of the composites led to the successful utilization of CM waste portion for making an eco-friendly reinforcing additive to form LDPE composites.