in this work recycled polyolefins from municipal solid wastes, composed of 95 percent polyethylene (pe) and 5 percent polypropylene (pp), are reinforced with chemicothermomechanical pulp fiber, and the resulting material is formed by compression and injection molding. tensile properties are presented as function of fiber concentration, fiber surface treatment with acetic anhydride and phenol-formaldehyde, and sample storage time in water. strength and touchness of the recycled polyolefins were increased with addition of non-treated fiber. addition of 30 percent fiber, by weight, in the polymer matrix, increased its young modulus up to 150 percent composites with 10 percent of treated fiber showed generally higher tensile properties than those containing 10 percent of non-treated fiber. for composites made with treated fiber, water sorption during storage time was lower and mechanical properties remained higher, compared with composites made from non-treated fiber