Microstructure and electrical properties of In 2 O 3 transparent thin films are analyzed on the basis of Structure Zone Model (SZM) proposed by Thornton. Thin films are deposited on glass substrate by RF magnetron sputtering with variation of substrate temperature (T s ) and argon gas pressure (P Ar ) . Microstructure of Zone I of SZM is observed with lowering of substrate temperature or increasing of argon pressure. The higher electrical resistivity of those specimens is due to micro-pores or voids between columnar grains. At the conditions of T s =450 ? C and P Ar =4.2mTor 4.2mTorr, the Zone II structure of SZM and the lowest electrical resistivity (2.1×10 ?2 Ωcm) are observed. The dense structure of columnar grains with faceting on growing surface and preferred orientation of (100) plane are observed in those specimens.