Null imaging ellipsometry was developed to show the net change in polarization state between two samples. This system has no moving parts for nulling and does not exhibit azimuthal dependence on the optical elements. Therefore, this system is fast in data acquisition and easy to operate. In addition, image uniformity can be improved through a normalization process. For a demonstration, this system was applied to annealing studies of indium oxide thin films. The results show that this system can visualize the temperature dependence of the annealing as well as the progress of the annealing over time.