This research presents a study about the influence of cement content and the piassava fibers (Attalea funifera) on the mechanical behavior of a fine-grained subgrade soil. Specimens of 10 cm in diameter and 20 cm in height were prepared from natural subgrade soil, 2wt.% of cement content, and 1,5wt.% piassava fiber from the Brazilian Amazon. Repeated load triaxial tests (RLT) with different stresses were conducted to provide permanent deformation behavior and the results were analyzed based on shakedown analysis. The aim was to verify if the addition of these fibers in a soil/cement matrix generates a significant effect on the mechanical behavior of the material regarding its permanent deformation, given the unsatisfactory geotechnical characteristics of the sedimentary soils in the Amazon region. It was found that the piassava fiber addition decreased the soil permanent deformation, although when mixed with cement, the permanent deformation was not significantly affected.