Transparent conducting indium tin oxide (ITO) thin films were deposited on glass substrates by magnetron sputter type negative metal ion source (MSNIS) using ITO target and then the effect of post deposition annealing temperature on the optoelectrical property of ITO film has been investigated. The resistivity and optical transmittance of ITO films that prepared at 70°C (without intentional substrate heating) with optimized deposition condition reached at 6.2×10-4 cm and 80%, respectively. As increasing post deposition annealing temperature, a rapid decrease is observed in the resistivity. The lowest resistivity of 1.7×10-4 cm and the highest optical transmittance of 83% were obtained at the post annealing temperature of 300°C. From the XRD and SEM measurements, the increment of the optical transmittance and conductivity by post deposition annealing treatment is attributed to the enhanced crystallinity of the ITO film.