Composites of high density polyethylene (HDPE) with the reinforcements of glass fiber (GF) and wood flour (WF) have been studied in this work. High-density polyethylene-grafted maleic hydride (HDPE-g-MAH) was used as a compatibilizer. In particular, the effect of GF, WF, and HDPE-g-MAH on the overall properties of GF/WF/HDPE composites (GWPCs in short form) was systematically studied. The results indicate that HDPE-g-MAH as a compatibilizer can effectively promote the interfacial adhesion between GF/WF and HDPE. By the incorporations of GF/WF, the heat deflection temperature can reach above 120 degrees C, and the water absorption can be below 0.7%, also the tensile strength, flexural strength, and impact strength of GWPCs can surpass 55.2 Mpa, 69.4 Mpa, and 11.1 KJ/m(2), respectively. (C) 2011 Wiley Periodicals, Inc. J Appl Polym Sci 123: 2084-2089, 2012