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The paper reports the effect of low-temperature annealing (up to 150°C) and light irradiation from a quartz mercury lamp (up to 20 min) on the structural, optical, and electrical properties of Indium tin oxide (ITO) films. 0.8 μm thick ITO films were obtained by RF magnetron sputtering of a commercial target on the optically transparent glass substrates in an argon atmosphere without heating. Information about the morphology of the ITO films' surface was obtained and the surface parameters were calculated using the method of atomic force microscopy. It has been found that the low temperature annealing for one hour and short-term irradiation with a quartz mercury lamp lead to an increase in the average size of crystallites and root-mean-square (RMS) surface roughness, a decrease in the resistivity of ITO films as well as an increase in the optical transparency in the visible spectral range. After annealing the ITO film at 150°C, the average crystallite size and RMS roughness of the surface increased approximately three times, and after 20 min irradiation – approximately 1.6 times, respectively. The lowest optical transparency in the visible spectral range among the studied experimental samples was found to be for the non-annealed and non-irradiated ITO films, whereas the highest – for the samples annealed at the highest temperature (150°C) and irradiated for 5 min with the light from the DRT-125 lamp. On the basis of the analysis of optical absorption spectra of ITO films, we detected an increase in their optical band gap from 3.59 eV for the unannealed film up to 3.66 eV with an increase in the annealing temperature of the samples up to 150°C. The resistivity of ITO films decreases with an increase in the annealing temperature up to 150°C and with an increase in the irradiation time with a light of the quartz mercury lamp up to 20 minutes. These results may be useful in the engineering of electronic devices based on the materials of low thermal stability. [ABSTRACT FROM AUTHOR]