The microstructures of Hg-based cuprate thin films have been studied using a scanning electron microscope and an energy dispersive X-ray spectrometer. Besides a rough surface, several types of defects including the HgCaO 2 phase are identified on those films made using a slow temperature ramping Hg-vapor annealing process. By ramping the sample temperature rapidly to the annealing temperature, the surface morphology of the film is significantly improved and the impurity phases, especially the HgCaO 2 phase, are effectively reduced.