This work is devoted to investigate the available agricultural Tunisian waste: the date pits as reinforcing filler for thermoplastic matrix. The chemical composition of this reinforcing filler is found to be comparable to nonwood plants: its content comprises of 13% of extractibles, 22% of lignin, and 61% of holocellulose. Then, the lignocellulosic filler was used to prepare different composites films using Brabender mixing device. A series of composite film was established by different loadings of the date pits waste with 10–50% of the filler in 10% as an interval. The ensuing composites materials were then characterized by several techniques such as the morphology of the composites, which was investigated using scanning electron microscopy. The thermal properties of prepared materials were studied using differential scanning calorimetry and thermogravimetric analysis. Finally, the mechanical and water absorption properties were involved. The obtained results indicated that date pits–based particles enhanced the thermomechanical properties of the thermoplastic matrix and demonstrated that this available lignocellulosic biomass can be considered to be a promising filler material.