Ceria doped yttria stabilized zirconia (ZrO2-CeO2-Y2O3 system) shows electron-ion mixed conduction at high temperatures under a reduced atmosphere. In this system, the electronic conductivity is caused by electrons, which may diffuse by hopping conduction between Ce4+ and Ce3+. We applied the electronic Raman scattering technique on the system in older to measure the concentration of Ce3+ in samples. For the X = 0.6 and 0.8 samples in [(ZrO2)(t-X) (CeO2)(X)](0.9)(Y2O3)(0.1), the oxygen partial pressure dependence of the electronic Raman intensities agrees well with that of the oxygen non-stoichiometry measured by thermogravimetry. From this result. it is confirmed that all of the introduced electrons at reduced condition are trapped at cerium centers in these materials. (C) 2000 Elsevier Science B.V. All rights reserved.