Changes of crystallinity and microstructure in undoped In2O3 films prepared by oxygen ion-assisted deposition were investigated using X-ray diffraction and scanning electron microscopy. The oxygen ion energy was varied from 60 to 500 eV during indium thermal evaporation. The crystallinity and microstructure of the films were closely related to the oxygen ion energy bombarded on the growing surface. Domain structure and preferential orientation in the [100] direction were obtained in the film deposited at 60 eV. Upon increasing the ion-beam energy to 500 eV, the domain structure was changed into the grain structure and the crystallinity became preferentially oriented along the [111] direction. Depending on the range of ion beam energy, the main effect of energetic ions on the growing surface of the film may be divided into two categories: the enhancement of adatom mobility and the creation of additional nucleation sites by lattice damage. Electrical properties of the deposited films were significantly dependent on the change of chemical composition and microstructure due to variation of ion beam energy. With increasing the ion beam energy, the electrical resistivity increased and the carrier concentration decreased. The film having the domain structure had larger mobility than other films having the grain structure, because a boundary scattering was reduced in the large size domains compared with the small size grains.