The effect of alkaline treatment on the properties of low-density polyethylene/natural rubber/water hyacinth fiber (LDPE/NR/WHF) composites was studied. LDPE/NR/WHF and LDPE/NR/WHFNaOH composites were prepared using a Brabender Plasticorder. The LDPE/NR/WHFNaOH composites showed higher tensile strength, Young's modulus, and melting temperature (T-m) but lower molar sorption and interparticle spacing (d) than did the LDPE/NR/WHF composites. Fourier transform infrared spectroscopy (FTIR) results confirmed that alkaline treatment removed hemicellulose and lignin in WHF, as evidenced by the disappearance of the absorption bands at 1732.79 and 1250.91 cm(-1). The LDPE/NR/WHFNaOH composites demonstrated less thermal stability and rougher surface after alkaline treatment.