We have investigated the structural, electrical and optical properties of $In_2O_3$ thin films deposited by RF magnetron sputtering and then annealed at $150^{circ}C$ and $300^{circ}C$ in vacuum. The structural and electrical properties are strongly related to annealing temperature. All the annealed $In_2O_3$ films are grown as a hexagonal wurtzite phase and the largest grain size is observed in the films annealed at $300^{circ}C$. The sheet resistance decreases with a increase in annealing temperature and $In_2O_3$ film annealed at $300^{circ}C$ shows the lowest sheet resistance of $174{Omega}/{Box}$. The optical transmittance of $In_2O_3$ films in a visible wavelength region also depends on the annealing temperature. The films annealed at $300^{circ}C$ show higher transmittance of 76% than those of the films prepared in this study.