The ¹⁸O tracer diffusion method was used to investigate oxygen diffusion in reactively dc-sputtered IrO ₂ films. The profile measurements were done by secondary ion mass spectrometry. For the investigation of the oxygen diffusivity in the samples a temperature range from 600 to 765°C was chosen. The oxygen tracer diffusion in IrO ₂ films was found to be described by an Arrhenius law with D ₀=(2.8±2.5) 10 ^-6m ²s ^-1 and an activation energy of E _a=(2.73±0.07) eV. It was also shown that the extrinsic oxygen diffusion is strongly influenced by the film preparation conditions, which is especially important for the application of IrO ₂ films as an oxygen barrier in future memory device applications.