This paper focuses on the geotechnical characterization of a clayey soil and its mixture with polypropylene fiber. The laboratory testing program was directed to: (1) analysis of the influence of fiber content and fiber length on the unconfined compression strength of a clayey soil in order to determine optimum parameters to be used in repeated-loading triaxial tests, and (ii) analysis of the influence of fiber on the resilient modulus of the clayey soil, according to the Brazilian standard DNER-ME 131/94. The laboratory testing data support that: (i) the mechanical response of the composite is fiber content and fiber length dependent; (ii) addition of fiber to the soil improves substanially its unconfined compression strength; and (iii) addition of fiber to the soil is also responsible for substantial decrease in its Mr values, and produces a composite that can be useful in road engineering practice