The formation of O_2~- ions on La_2O_3/MgO Catalyst for oxidative cou-pling of methane and its interaction with CO_2 have been studied by EPR andFT-IR.The O_2~- ions with EPR parameters valued at g_(xx)=1.999,g_(yy)=2.018,g_n=2.061;A_(xx)=5.0G,A_(yy)=7.6G,are unstable at 573 K under vacuum.They could react with CO_2 at room temperature leading to the decrease of theirEPR signal intensities and the appearance of a new carbonate species with IRabsorption bands at 1628cm~(-1) and 1335 cm~(-1),in comparison with the CO_2 ab-sorption on the O_2~-free sample.It appears unlikely that the O_2~- ions are theactive oxygen species for the activation of methane. The formation of O_2 ~ ions on La_2O_3 / MgO Catalyst for oxidative cou-pling of methane and its interaction with CO_2 have been studied by EPR and FT-IR.The O_2 ~ ions with EPR parameters valued at g_ (xx) = 1.999, g_ (yy) = 2.018, g_n = 2.061; A_ (xx) = 5.0G, A_ (yy) = 7.6G, are unstable at 573 K under vacuum. They could react with CO_2 at room temperature leading to the decrease of theirEPR signal intensities and the appearance of a new carbonate species with IRabsorption bands at 1628 cm -1 and 1335 cm -1, in comparison with the CO 2 ab-sorption on the O 2 ~ -free sample. It appears unlikely that the O 2 ~ - ions are the active oxygen species for the activation of methane.