We have investigated the structural, electrical and optical properties of In2 O3 thin films deposited by RF magnetron sputtering and then annealed at 150℃ and 300℃ in vacuum. The structural and electrical properties are strongly related to annealing temperature. All the annealed In2O3 films are grown as a hexagonal wurtzite phase and the largest grain size is observed in the films annealed at 300℃. The sheet resistance decreases with a increase in annealing temperature and In2O3 film annealed at 300℃ shows the lowest sheet resistance of 174 Ω/□. The optical transmittance of In2O3 films in a visible wavelength region also depends on the annealing temperature. The films annealed at 300℃ show higher transmittance of 76% than those of the films prepared in this study. (Received September 27, 2011; Revised October 14, 2011; Accepted October 20, 2011)