The results of the investigations on the influence of CeO2 adding on the transformation of the metastable Al2O3 forms obtained by thermal treatment of xerogels are presented. It is established that in the presence of CeO2 the process of the formation of a stable phase of α-Al2O3 (corundum) takes place in a wider temperature range and is accomplished at a higher temperature (1300°C). It is suggested that the revealed mismatches on the diffractograms between the intensity values of the main analytical peaks of the corundum and its content in the samples are associated with the effect of screening caused by the differences in the mass coefficients of absorption of (μ) CeO2 and Al2O3.