This experimental study reports the mechanical behavior of a reinforced and unreinforced clayey soil with the addition of short sisal fibers randomly distributed submitted to natural aging by their exposure to diverse environmental conditions. This vegetable fiber was chosen because it has good mechanical properties and the need for new renewable materials, which can successfully replace synthetic fibers. A series of unconfined compressive strength tests was performed on clay and clay-fibers samples at zero time (sample control) and on composites exposed to agents from the external environment for up to 8 months to seek to establish patterns of behavior that might explain the influence of the addition of sisal fibers, relating it to the shear strength parameters of the soil. The tests were performed on samples subjected to a maximum dry density and optimum moisture content, fibers content in proportions of 0 and 0.5% of the dry weight of the soil and the fibers lengths of 25 mm. Through the obtained results, it was observed that the addition of sisal fibers randomly distributed leads to significant improvements in the mechanical properties of the soil. It was possible to identify that the effects of natural aging had a significant effect on the mechanical behavior of the vegetable fibers, which consequently affected the mechanical behavior of the clay-fiber composites.