The effect of different concentrations of polyethylene-grafted-maleic anhydride (PE-g-MAH) in recycled high-density polyethylene/water hyacinth fiber (rHDPE/WHF) composites was studied. RHDPE/WHF composites with different concentrations of PE-g-MAH were prepared using Z-blade mixer at 180 A degrees C with the rotor speed of 50 rpm. The results indicated 6 wt% of PE-g-MAH showed the highest tensile strength and Young's modulus but lowest water absorption compared to other concentration of PE-g-MAH. The SEM morphology of 6 wt% of PE-g-MAH displayed better fiber dispersion and less fiber pull out than other concentration of PE-g-MAH. Moreover, FTIR analysis also showed the presence of ester carbonyl group and reduction of OH group in rHDPE/WHFPE-g-MAH composites than uncompatibilized composites.