Using a scanning microwave microscope, we investigated the local electrical properties of epitaxial CaRuO3 thin films. The films showed a metal–insulator transition depending on the growth temperature and their thickness. We observed spatially separated highly conducting and poorly conducting regions in the films grown at a high temperature of 800 °C, which showed insulating behavior. The conduction in the CaRuO3 thin films with insulating behavior is percolative through the highly conducting regions and is closely related to this two-phase behavior. © 2002 American Institute of Physics.