We report the fabrication and characterization of indium oxide (In2O3) thin-film transistors (TFTs) with excimer light irradiation and heat treatment by solution process. We evaluated the impact of varying the irradiation time of excimer light and the temperature of heat treatment on the In2O3 thin films. The combined process of excimer light irradiation and thermal treatment reacted with the formation and decomposition of OH groups. As a result, we were able to efficiently produce In2O3 in this fabrication process. Transfer characteristics of In2O3-TFTs with excimer light irradiation and heat treatment showed better than these of In2O3-TFTs with heat treatment, and On/Off ratio of the In2O3-TFT with excimer light irradiation and heat treatment was 3.26×104. Furthermore, the transfer characteristics of In2O3-TFT irradiated by excimer lamp in O2 atmosphere were improved, and O2 in the atmosphere during excimer light irradiation was important for the low-temperature formation of the thin films.