Cellulose fiber waste from the white cellulose pulp purification process produced by the company Nipo Cellulose-Brazil (CENIBRA) was used in the preparation of composites with polyurethane. An elastomeric polyurethane based on polyether poly(tetramethylene glycol) and 4,4-diphenylmethane diisocyanate was used as polymeric matrix. Structural, thermal, and morphological characterization of the composites was carried out by infrared spectroscopy, thermogravimetry, differential scanning calorimetry, and scanning electron microscopy. The results indicate that interfacial interaction between the cellulose fiber residue and the polyurethane matrix occurs and that cellulose waste is a promising reinforcement for polyurethane composites. (c) 2005 Wiley Periodicals, Inc.