AbstractHigh-density polyethylene (HDPE)/ethylene-propylene-diene monomer (EPDM) blend was prepared by mixing HDPE and EPDM in an internal mixer. Kenaf fibers were then added to the mixture with a few minutes of mixing. The tensile properties of the HDPE/EPDM/kenaf composites were investigated using tensile testing and scanning electron microscopy. Treated kenaf bast powder was prepared using hydrochloric acid (HCl). Hydrolysis was carried out to study the effect of HCl on the structure, composition, and properties of the fibers. HCl treatment removed the impurities in the fibers, resulting in smooth fibers with a small particles size. Fourier transform infrared analysis showed a reduction in lignin, wax, and hemicellulose but no modification in surface chemical composition. The treated filled HDPE/EPDM composites had high tensile strength, elongation at break, and modulus than the untreated filled HDPE/EPDM composites.