Homogeneous mixtures of nanocrystalline powders of (NiO + Ni)/YSZ were obtained by combustion synthesis, and used to prepare Ni/YSZ cermets for symmetrical cermet/YSZ/cermet cells. These cells were prepared by co-pressing, co-firing at 1450 degreesC, and reduction in 10% H-2-90% N-2 at 800 degreesC. The resulting Ni/YSZ cermets are porous and adherent to the electrolyte, and its metallic and ceramic components are uniformly distributed. Impedance spectroscopy was used to characterise these symmetrical cells in atmospheres containing H-2 and H2O. The impedance spectra show that the electrode reactions comprise at least two processes with different relaxation frequencies. The low frequency contribution of the polarisation resistance is very dependent on the partial pressures of H-2 and H2O. The contribution at higher frequency is mainly dependent on temperature,