The effects of (a) the chemical modification of water hyacinth fiber by poly(vinyl alcohol) (WHF-PVA) and (b) loading on the properties of low-density polyethylene (LDPE)/(natural rubber (NR))/(water hyacinth fiber (WHF)) composites were studied. Mechanical properties, water absorption behavior, morphology, and thermal properties were examined; X-ray diffraction and infrared spectroscopic analysis were done. The results indicated that LDPE/NR/WHF-PVA composites had higher values of tensile strength, Young's modulus, melting temperature, and water absorption resistance but lower elongation at break than LDPE/NR/WHF composites. The LDPE/NR/WHF-PVA composites had better interfacial adhesion between the matrix and the fibers than LDPE/NR/WHF composites, as shown by SEM results. The LDPE/NR/WHF-PVA composites exhibited lower interparticle spacing than LDPE/NR/WHF composites, a feature which enhanced the interparticle interaction between the water hyacinth fibers and the LDPE/NR matrix. J. VINYL ADDIT. TECHNOL., 19:47–54, 2013. © 2012 Society of Plastics Engineers