Polyurethane (PU)/Clay nanocomposite rigid foams were synthesized with modified layered silicate clay (organoclays, Cloisite 30B). PU foams were prepared by a batch reaction injection molding process. Organoclay was dispersed first in the isocyanate component using an ultrasonic homogenizer and then mixed with polyol and physical blowing agent mixture to produce nanocomposite PU foams. To study the reaction possibility between cloisite 30B and isocyanate as well as the effect of sonication on the reaction, Fourier transfer infrared (FTIR) analysis was conducted. The dispersion of organoclay in the rigid PU/clay nanocomposite foams was analyzed by wide angle X-ray diffraction (XRD). The microstructure of the foams was studied by an optical microscope and image analysis software. It was concluded that with increasing of nanoclay content the cell size is decreased and the cell size distribution is narrowed. The mechanical properties of pure and nanocomposite foams were examined by compression test. The data obtained from the compressive stress-strain curves reveals that the strength and modulus of polyurethane foam increase by addition of organoclay up to 1wt% and then decrease. Thermal conductivity coefficient (k-factor) of rigid PU nanocomposite and neat foams was measured by a simple transient method. The thermal conductivity results demonstrated that the polyurethane foam k-factor continuously decrease by addition of organoclay. It can be attributed to the reduced cell size as well as narrow cell size distribution in of nanocomposite foams.