In this work we studied indium zinc oxide (IZO) thin films deposited by r.f magnetron sputtering at room temperature. The films were annealed at high temperature (1100 K) in vacuum, and the oxygen exodiffusion was monitored in-situ. The results showed three main peaks, one at approximately 600 K, other at approximately 850 K and the last one at 940 K, which are probably from oxygen bonded in the film surface and in the bulk, respectively. The initial amorphous structure becomes microcrystalline, according to the X-ray diffraction. The electrical conductivity of the films decreases (about 3 orders of magnitude), after the annealing treatment.