Novel rigid polyurethane nanocomposite foams have been prepared by the polymerization of a sucrose-based polyol, a glycerol-based polyol and polymeric diphenylmethane diisocyanate in the presence of cellulose whiskers. Varying amounts of sulfuric acid hydrolyzed cellulose whiskers (0.25, 0.50, 0.75 and 1.00 wt%) prepared from a commercial fully bleached softwood kraft pulp were incorporated to investigate the effect of its dosage on the mechanical and thermal properties of polyurethane nanocomposites. Fourier transform infrared spectra of the nanocomposite foams suggested that additional hydrogen bonds were developed and crosslinking occurred between the hydroxyl groups of cellulose whiskers and isocyanate groups which increased the phase separation of soft and hard segments in the polyurethane. The closed cells of control foam and nanocomposite foams were homogeneously dispersed and the cell sizes were approximately 350 microm in diameter as observed by scanning electron microscope. A substantial improvement of mechanical properties at low whisker content (< or = 1.00 wt%) was obtained, especially the compressive strength and modulus at 1.00 wt% whiskers content which were increased by 269.7% and 210.0%, respectively. Thermal stability of the nanocomposites was also enhanced as determined by differential scanning calorimetry and thermogravimetric analysis.