Composites made from a stryrene/unsaturated polyester thermoset matrix and woodflours from different wood species have been prepared and tested. Pine (Pino Eliottis), eucaliptus (Eucaliptus Saligna) and marmelero (Ruprechia Laxiflora), a softwood and two semihard woods respectively, were selected for this study because of the availability and local abundance. The particles were used untreated and chemically modified with maleic anhydride (MAN). Thermogravimetric analysis and analytical techniques were used in the characterization of untreated and treated flours. Dispersion of the fibrous particles, as well as maximum filler concentration (accompanied by complete wetting of the wood fibers) was dependent on the treatment and on the wood species utilized. Bending and compression tests indicated some improvement in the performance of the composites, if the woodflour was previously esterified. Scanning electron microscopy (SEM) allowed to observe changes in the fracture surfaces due to MAN treatment of the fibers.