In this study, sawdust filler from White Cham washed with distilled water in order to increase their compatibility with a polymeric matrix, and their properties were compared with unwashed sawdust used as filler forUnsaturated Polyester (UPE) resin used with three volume fractions (20, 30 and 40%). Samples of unwashed and washed sawdust were characterized by tensile and thermal conductivity. The treatment with water was effective in increasing the surface roughness, and crystallinity, thereby increasing the thermal conductivity of the washed sawdust/UPE composites. However, results showed that the addition of washed sawdust/UPE composite provided an improvement in mechanical properties of composites. The maximum percentage in improvement of tensile strength, toughness and elongation at break were (7.7, 23.1 and 4.4%) respectively at (Vf=20%) in comparison with unwashed sawdust/UPE composites. Also, the results showed an increase in volume fraction of sawdust decrease the mechanical properties and thermal conductivity.