A 10 wt oil palm empty fruit bunch (EFB) fiber reinforced high density polyethylene composites were developed and tested for mechanical properties and water absorption. The fibers were treated with various percentages of alkali, acrylic acid and two types of silanes, α- methacryloxypropyltrimethoxysilane (MTS) and vinyltriethoxysilane (VTS). The fibers treated with 10 alkali, 3 MTS, 3 VTS and 5 acrylic acid showed enhanced tensile strength and modulus compared with that of the untreated fibers reinforced composites. The chemical treatments showed approximately 6 and 18 increase in flexural strength and modulus, respectively. The chemical treatments were found to be effective to reduce water absorption of the composites developed. Composites developed from fibers treated with 3 MTS showed highest reduction in water absorption and relatively higher increase in tensile strength and modulus compared to those fibers treated with other types of chemicals and untreated fibers. © The Author(s), 2010.