Aqueous emulsion of polyurethane (PU) ionomers were reinforced with hydrophobic nanosilica to give composites. The aqueous emulsion was stable and the particle size increased as the content of hydrophobic nanosilica was increased. The reinforcing effect of nanosilica in mechanical properties of these composites were examined by dynamic mechanical and tensile tests, and the Shore A hardness was measured. Enhanced thermal and water resistance and marginal reduction in transparency of these composites were observed compared with pristine polymer. These results were similar with those of our previous studies on waterborne PU/organoclay nanocomposites.