The effects of Mn/Na2WO4, Li, and CaO loading on the monoclinic Sm2O3 catalyst were investigated for the oxidative coupling of methane using O-2 or N2O as an oxidant. The catalysts were prepared by wet impregnation method and characterized by XRD, BET, CO2-TPD, and XPS analysis. Impregnation of Mn/Na2WO4 on monoclinic Sm2O3 resulted in the formation of Sm2-xMnxO3 phase, decreasing the catalytic performance. Li impregnation increased the C-2 selectivity but decreased the catalytic activity. The SmLiO2 formation increased the catalytic activity and selectivity. High amounts of CaO impregnation increased the C-2 selectivity of monoclinic Sm2O3 without a loss in catalytic activity. 6Li/m-Sm2O3 were found unstable due to the Li loss from the catalyst. The 15CaO/m-Sm2O3 was quite stable and showed 8.2% ethylene yield with N2O use, much higher than that was obtained with the well-known 2Mn/5Na(2)WO(4)/SiO2 and 4Li/MgO catalysts. N2O was more selective than O-2 as an oxidant and enhanced ethylene formation.