Polystyrene (PS) composites containing different concentrations of Palm Trees Fibers (PTF/PS) have been prepared by hot mixing process using Plasti Corder machine. PTF surface have been treated by PS solution to optimize the adhesion between PTF and PS in PTF/PS composite. The study of the abrasion, water absorption and the mechanical properties of the treated and untreated PTF/PS composites showed a significant improvement for the treated composites. The value of the modulus of the elasticity increased by the PS solution treatment from 1.1 GPa to 3.45 GPa for 60% fiber concentration in PTF/PS composites.