Indium tin oxide (ITO) thin films were deposited on glass substrates via sol-gel spin coating process from a mixed solution of Indium (III) acetylacetonate and Tin (IV) iso-propoxide. Then, ITO thin films were fired at 500 degrees C, and then annealed at 500 degrees C for 30 min with the sequential annealing process; Vacuum -> N-2-> Ar/H-2, N-2-> Ar/H-2 and Ar/H-2 gas. The effects of the different annealing processes on the surface morphologies and sheet resistance of ITO thin films were investigated. Sheet resistance values of ITO thin films treated under Vacuum -> N-2-> Ar/H-2, N-2-> Ar/H-2 and Ar/H-2 annealing process were 1.25 kohm./sq., 3.18 kohm/sq. and 4.92 kohm/sq., respectively. Actually, the sequential atmosphere gases and non-oxidizing gas, which were used in annealing process influenced the microstructural features or surface morphologies of ITO thin films: grain size and surface roughness. Thus, it was presumed that the sequential annealing condition influenced the densification behavior in the microstructural evolution of ITO thin films.