By using the sputtering process, we made the IrMn based specular spin valve system, whose nano-oxide layer (NOL) was formed by natural oxidation. After thermal annealing at 305 and 410 °C, the thermal stability of the specular spin valve was observed. We found that the highest magnetoresistance (MR) ratio of about 12 % MR was produced after optimum annealing at 305 °C but the sample annealed at 410 °C also had a high MR ratio about 10 %. It is superior to other studies at this temperature. Based on the AES and XPS results, we could conclude that this enhanced thermal stability was due to the stable Cu layer between the pinned layer and free layer and to the NOL as a diffusion barrier for the Mn.