In2O3 thin films were grown by the chemical spray pyrolysis (CSP) method using the pneumatic spray set-up and compressed air as a carrier gas. Aqueous solutions containing InCl3.4H2O were deposited onto preheated glass sheets at substrate temperatures Ts=423–573K. X-ray differection (XRD) analysis confirmed the cubic bixbyite structure of indium oxide. The preferred growth orientation along the (211) plane for thin films. The crystallite size extracted from the XRD data corroborates the changes in full width at half maximum due to the variation in substrate temperature. It was shown that grain size of In2O3 thin film was (30)nm. Optical properties of In2O3 was studies and showed that the optical parameters (n, k α) were affected by substrate temperature.