ABSTRACT This work evaluated the influence of the concentration of NaOH (100, 200 and 300 g/L NaOH) in the mercerization process at 25 °C for 1 h, and of the percentage (15, 20 and 25% m/m) of Mauritia flexuosa fibers on impact resistance in a polyester matrix composite. The polyester matrix composite was obtained by the compression molding process, at a constant pressure of 24 MPa. The obtained plates had a dimension of 130 mm long x 80 mm wide x 3.4 mm thick. Specimens for the impact assay were extracted from the obtained plates under the EN ISO 179-1 standard. Likewise, the fiber-reinforced composites without treatment were also evaluated, all the fibers were characterized before and after the NaOH treatment by means of the chemical characterization of the fiber, absorption percentage, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy ( FT-IR). The result...