In2O3-ZnO (IZO) thin films were prepared on Pyrex glass by using a radio frequency magnetron sputtering technique and their properties were studied in terms of the annealing process (temperature and atmosphere). The resistivity of as-deposited films grown at room temperature was as low as 4.65 × 10-4Ωㆍcm and the average transmittance in the visible region was more than 82 %. The correlation between the resistivity and annealing process was investigated using atomic force microscopy, X-ray diffraction, and inductively coupled plasma mass spectrometry. The resistivity of the IZO film after annealing increased greatly because the film structure was changed from amorphous to a crystalline phase. The evaporation of In and Zn and the disappearance of oxygen vacancy are two possible reasons for the high resistivity after high-temperature annealing. It could be concluded that IZO thin films as a transparent conducting oxide might be suitable for flexible displays and solar cells that require low-temperature annealing.