The effects of various types of compatibilizers on the mechanical properties of high-density polyethylene/wood flour (HDPE/WF) composite were investigated. Functionalized polyolefins such as maleated and acrylic acid grafted polyethylenes, maleated polypropylene (PPgMA) and styrene-ethylene/butylene-styrene triblock copolymer (SEBSgMA) were incorporated to reduce the interfacial tension between the polyethylene matrix and the wood filler. Among them, it was found that maleated linear low-density polyethylene (LLDPEgMA) gave maximum tensile and impact strength of the composites, presumably because of better compatibility with the HDPE matrix. Similar but less enhanced improvements in the mechanical properties, depending on the compatibilizer loading, were seen for the SEBSgMA system. Whereas acrylic acid grafted high-density polyethylene (HDPEgAA) and maleated polypropylene (PPgMA) only slightly improved tensile modulus and tensile strength; and they both increased with increasing loadings of compatibilizers. A scanning electron microscopic study was employed to reveal the interfacial region and confirm these findings. In addition, dynamical mechanical thermal measurements also revealed the interaction between filler and matrix, and FTIR spectroscopy was used to assign the chemical fixation and the various chemical species involved at the surface of the wood fillers before and after surface treatment.