Cellulose obtained from water hyacinth (Eichhornia crassiper) fibers were blended with low-density polyethylene (LDPE), forming LDPE / water hyacinth fiber WHF) composites. In this work, the effects of filler loading on the mechanical, morphological, and water absorbent properties of this composite were investigated. Two types of fibers were used, namely treated fibers (where some of the fibers were treated with coupling agent) and untreated fibers. It was found that the tensile strength of the composites increased with increasing of the filler concentration. The presence of coupling agent improved the interfacial bonding between the matrix and water hyacinth fibers, as evidenced by scanning electron microscopy (SEM). In addition, fiber loading increased the water absorption of the composites. The treated fibers showed a reduction in water uptake.