Indium oxide (In2O3) thin lms were deposited on glass substrate by varying substrate temperature in the range of 400600• C using the spray pyrolysis technique. In this research, physical properties of indium oxide thin lms were studied and then nanocrystalline sizes at dierent substrate temperature were deeply compared and investigated. All lms were characterized at room temperature using X-ray diraction, scanning electron microscopy, atomic force microscopy, photoluminescence, the Hall eect and UV-visible spectrophotometer. The optimal substrate temperature to obtain lms of high crystallographic quality was 575• C, for this temperature, the electrical resistivity was in the order of ρ = 0.147 Ω cm. For comparing optical transmittance and electrical conductivity the best gure of merit of the lms was achieved at 575•