A multiscale study of the high temperature oxidation effects on high purity polycrystalline nickel behaviour is presented. In situ tensile tests have been carried out at room temperature on preoxidised thin foils. The results obtained lead to a better understanding of the strengthening effect of the oxide layer. Detailed examinations of the metal microstructure are also made after high temperature oxidation treatment. Atomic Force Microscope (AFM), Secondary Ion Mass Spectroscopy (SIMS), Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM) are used to characterise the microstructure. Formation of voids at grain boundaries as well as vacancy injection are then discussed.