Nanosized ITO powder was fabricated by homogeneous precipitation which used formamide as a precipitator. ITO thin film was deposited by RF magnetron sputtering using ITO target which was prepared by sintering of nanosized ITO powder. From the accelerated degradation test with stress factor of temperature, the lifetime estimate, degradation rate/degree, activation energy and etc. were calculated. It was showed that under thermal condition, the prominent failure mechanism of degradation was the decrease of oxygen vacancies due to oxidation of ITO thin film.