A method for determining the chemical diffusion coefficient and the surface reaction resistance for oxygen in mixed conducting oxides has been developed. The method is based on impedance analysis of a zirconia oxygen pumping cell containing a sample of the oxide. For La0.85Sr0.15MnO3 the reaction resistance at 1000 degrees C in air is measured as 200 Omega cm(2), which corresponds to a surface exchange coefficient of 5x10(-6) cm/s. The value of the chemical diffusion coefficient under the same conditions is 2x10(-9) cm(2)/s, and the thermodynamic enhancement factor is calculated as 200. The corresponding self-diffusion coefficient obtained by this method is then 1x10(-11) cm(2)/s compared with the values of 3x10(-13) cm(2)/s, 4x10(-14) cm(2)/s obtained by O-18/O-16 exchange experiments on La0.65Sr0.35MnO3 at 900 degrees C.