The study of the influence of molecular oxygen on N2O decomposition under conditions of oxidative coupling of methane (OCM) and on the simple reaction of N2O decomposition (without methane) was carried out over SrO and Li/Bi2O3. It was found that molecular oxygen caused the decrease in the rate of N2O decomposition over all the catalysts studied under conditions of OCM. However, the overall catalytic activity over Bi-containing catalysts are significantly lower than that for SrO. Poisoning by molecular oxygen was established over Li/Bi2O3 for N2O decomposition without methane. Over SrO molecular oxygen was not shown to inhibit the decomposition of nitrous oxide in the absence of methane. It was established that the defect structure of SrO was changed under catalytic conditions. The participation of structural defects for N2O decomposition and CO2 formation was proposed.