XPS characterization was carried out for the solid-solution xalpha-Fe2O3-(1-x)ZrO2 which is a potential low temperature oxygen gas sensing, material. The significant variation of relative intensity of the two peaks in 0 Is spectra provides us a unique way to estimate the oxygen vacancy concentrations of xalpha-Fe2O3-(1-x)ZrO2 with x ranging from 0 to 0.3. The estimation result from XPS coincides with the calculated values from the substitutional model. The relationship between the sensitivity of the fabricated oxygen gas sensor and the oxygen vacancy concentration in the sensing material was established. (C) 2002 Elsevier Science B.V. All lights reserved.