In mixed electronic and ionic conductors O-2 (-)/e(-) (MIEC), where the electronic conductivity is dominant, the determination of the oxygen diffusion coefficient is an essential feature. In the present paper, the oxygen chemical diffusion coefficient,60 of a MIEC oxide has been evaluated using the conductivity relaxation method, in the temperature range 773-1173 K. Samples of La2Cu0.5Ni0.5O4 + delta were selected because of the high value of their surface exchange coefficient. In addition, the oxygen diffusion coefficient D* was determined from the 180 tracer diffusion profile. Finally, the oxygen partial pressure dependence of this compound was determined by thermogravimetric analysis (TGA). On the basis of these three independent experiments, the model of ambipolar diffusion, which describes the diffusion in mixed oxide, has been experimentally verified. For such a determination of the intrinsic diffusion characteristics, dense samples are required.