Abstract: The surface acidity of chromia-promoted magnetite shift catalyst, (Fe,Cr)₃O₄, was studied by TPDtechnique. The experimental results revealed the variability of surface structure of the catalyst. The adsorption of pyridine rearranges the surface structure and accelerates the establishment of a stable adsorption state of pyridine on the surface.There exist mainly two kinds of acidic site, α and β,on the surface of catalyst. The content of surface oxygen of the catalyst treated by COat higher temperature will be lower and the TPDpeaks of pyridine absorbed on the catalyst, which had been treated by COat different temperatures, varied regularly: the higher the treated temperature, the taller the peak α and the shorter the peakβ. This fact in combination with the shape and the position of peaks α and β had led to the conclusion that the peaks α and βare relative to Fe²⁺ site snd Fe³⁺ site, respectively.The activation energy of desorption of pyridine, E_d on the site βhas been determined by consulting table method. Its value is 278.8 + 13.8kJ/mol.