Highly transparent and conductive thin films of ZnO doped with a rare-earth element, Sc or Y, have been prepared by d.c. magnetron sputtering using a powder target. The resistivity of the ZnO:Sc thin films was always lower than that of the ZnO:Y thin films; a resistivity in the order of 10(-4) Omega cm was obtained in these films. The resistivity of the ZnO:Sc thin films decreased as the Sc2O3 content was increased up to about 2 wt.%; any further increase of the Sc2O3 content caused the resistivity to increase. A resistivity of 3.1 Angstrom X 10(-4) Omega cm was obtained in ZnO:Sc thin films prepared on a glass substrate at a temperature of 200 degrees C with a Sc2O3 content of 2 wt.%. An average transmittance of above 85% in the visible range was obtained for doped ZnO thin films. The electrical and optical properties, as well as the thermal stability of resistivity, of the ZnO:Sc thin films were comparable to those of ZnO:Al.