Oxidative coupling of methane was carried out over various metal oxide catalysts (MOO, Y2O3, La2O3, Sm2O3 and Ho2O3) modified with Li+ and the catalytic performance of the catalysts was examined. Li+-added Y2O3 catalyst, which was prepared by impregnation Of Y2O3 with an aqueous solution of Li2CO3, was the most effective for the formation of ethene and ethane among all the catalysts tested in this study. However, the Li+-added Y2O3 catalyst was deactivated during the reaction at 1053 K, i.e., selectivities to ethene and ethane decreased and those to CO and CO2 increased with time on stream. X-ray diffraction pattern and Raman spectrum of the Li+-added Y2O3 catalyst showed that Li species was mainly localized on the surface of the catalyst and bulk structure of the catalyst did not change by the addition of Li+. Therefore, this deactivation of the Li+-added Y2O3 catalyst was caused by the elimination of Li species from the catalyst surface during the oxidation, due to the weak interaction between Li species and Y2O3. On the other hand, Li+-added Y2O3 catalyst, which was prepared by impregnation of Y(OH)(3) with an aqueous solution of Li2CO3, showed almost the same initial catalytic performance as that of the catalyst prepared from Y2O3 and Li2CO3. The catalyst prepared from Y(OH)(3) was more stable during the reaction compared to that of Y2O3. The catalytic stability of the former results from a homogenous dispersion of Li species in the catalyst bulk.