High temperature current-voltage characteristics were investigated with a Nb doped SrTiO 3 (Nb–STO) single crystal. The conductivity of the 0·5 wt% Nb doped SrTiO 3 showed high n-type conductivity with a negative temperature coefficient. The Pt/Nb–STO interface freshly prepared by laser ablation at 973 K in high vacuum condition showed ohmic behavior. However, it turned to show a Schottky type non linearity when annealed in oxygen gas at temperatures higher than 773 K. The I–V curve in the forward direction was well fitted with the equation based on the thermionic emission model. At high temperatures, the I–V behavior was dependent on the oxygen partial pressure. The lower oxygen partial pressure resulted in a lower barrier height. The change in the I–V curve with oxygen potential was almost reversible at 873 K, and was frozen below 673 K. Those phenomena suggested that the Schottky barrier formation at the Pt/STO interface has a strong relation with the oxygen transport in Nb–STO.