This research focuses on recycling agriculture waste to produce a composite material that could be utilized for different purposes. The current work is interested to study the role of the interface and the mechanism to enhance the bonding between this type of fibers with resin. This paper introduces an idea to perform chemical treatment with (Ethanol, HCl, NaCl, NaOH) solutions on the fibers to improve the adhesion. The natural fibers named (wheat and barley legs) were used as a reinforcing phase within the polyester resin as a matrix phase to prepare the composite material. The composite material was prepared by hand lay-up method with weight fraction (40%) of natural fibers. Mechanical tests of these composite such as impact, flexural strength, compression tests were carried out. It is found that the treating of these fibers with ethanol gives positive results and enhances the adhesion of the interface between the fibers and the matrix of the composite which leading to an increase in the strength of composite under effect the applied force.