Polyurethane/organophilic montmorillonite (PU/OMT) nanocomposites based on polyether, organophilic montmorillonite, phenylmethane diisocyante, diglycol, and glycerine were synthesized and characterized by x-ray diffraction (XRD). Delaminated or intercalated structures in polyurethane/OMT nanocomposites with different OMT content were found. The mechanical, thermal, and inflammability properties of PU/OMT nanocomposites were investigated through tensile, thermogravimetry, differential scanning calorimetry, and cone calorimetry experiments. It is shown that polyurethane/OMT nanocomposites have enhanced tensile strength, improved thermal stability, and flame retardant properties relative to bulk polyurethane. The tensile strength of PU/OMT with 4.7 wt% OMT content was double compared to that of bulk PU. The thermal and flame retardant properties of PU/OMT were enhanced compared to that of bulk PU. The thermal and flame retardant properties of PU/OMT increased with increasing OMT content.