A modified clay was used to prepare waterborne polyurethane (WPU)/clay nanocomposite dispersions in this study. XRD and TEM examinations indicate that the clay platelets are exfoliated. Moreover, AFM phase image of the WPU/clay film shows that the isolated clay-rich phases are surrounded by a continuous WPU-rich phase. Clay does not influence the location and peak broadness of the T-g of soft segment domains in the WPU/clay films. However, clay raises the T-g of hard segment domains, which is probably due to the ionic interactions between the clay and hard segments of WPU. These ionic interactions could be evidenced by IR spectra of the WPU/clay nanocomposites. The WPU/clay dispersion with higher clay content exhibits a larger average particle size, a less negative zeta potential, and a higher viscosity, whereas the corresponding cast film possesses lower volumetric and surface electrical resistances. The volumetric and surface electrical resistances of the WPU/clay nanocomposite film are nearly identical. This indicates that clay platelets do not migrate to the surface regions of WPU/clay films because of the above-mentioned ionic interactions. In addition, the incorporation