This study evaluated physical and mechanical properties of the wood plastic composite panels made from dry-blended rubberwood fiber-polypropylene (PP) powder formulations using a conventional flat-press process under laboratory conditions. Three levels of rubberwood fibers (Hevea brasiliensis), 40%, 50%, and 60% based on the composition by weight, were mixed with the PP powder without and with 3% (based on weight) maleic anhydride grafted PP (MAPP) as a coupling agent. Water resistance of the panels was negatively influenced by the increasing wood fiber content. The modulus of rupture of the panels significantly increased with the increase in the wood fiber content from 40 to 50wt% and then decreased as the fiber content reached 60wt% but this decrease was not significant. The modulus of elasticity of the panels increased with the increase in fiber content from 40 to 60wt%. Internal bond strength and screw withdrawal resistance declined with the increase in fiber content from 40% to 60wt%. The formulations with MAPP were found to have higher strength and better water resistance.