Buriti (Mauritia flexuosa) is a robust palm tree, abundant in the northeast of Brazil. Buriti fibers are rich in cellulose and have potential applications in polymer reinforcement. In this work, buriti fibers were used: as received, mercerized and in a silanized form. They were combined with cardanol–formaldehyde thermoset resin and hot-pressed to form composites. Scanning electron micrograph showed that the mercerization process induced a roughness onto the fiber surface. Dynamic mechanical analyses showed that increasing the fiber content provides an improvement in the rigidity of the composites. The mercerization treatment showed the best results for fiber/matrix adhesion.