Due to many advantages of using natural resources, natural fibers have been used recently as a method of providing added strength and ductility to reinforced polymer composites. This is mainly due to their availability, renewability, low density, cost effectiveness as well as satisfactory mechanical properties. This paper presents fabrication and experimental characterization analysis of mechanical properties of a class of bio-composite in which polypropylene (PP) and low density polyethylene (LDPE) are reinforced with date palm frond fibers. Bio- composite sheets were fabricated with controlled processing parameters based on small factorial design in order to develop a statistical model for response using fractional design of experiment. In a Design of Experiment (DoE) procedure, we identify three different factors along with three different levels; fiber volume fraction (20, 40, and 60 vt. %), alkali treatment (10, 15, and 20 Wt. %), and treatment time (2, 4, and 6 h). In this study, NaOH alkali solution is used to modify the fiber properties and improve surface characteristics. The tensile and flexural strengths of specimens prepared according to ASTM standards were measured by direct physical testing. Also, the Response Surface Methodology (RSM) is adopted to analyze interactions among the input factors and their effect on overall mechanical properties of the fabricated composite. Results revealed that fiber length and percentage of NaOH treatment have a significant impact on the composite properties. The date palm frond reinforced polypropylene composites could serve as a potential material in broad range of industrial applications in which high strength is not a main design requirement.