Single-phase　perovskite-like　oxides　NdSrCu1-xCoxO4-delta　and　Sm1.8Ce0.2Cu1-xCoxO4+delta　(x　=　0,　0.2,　and　0.4)　were　prepared　using　the　citric　acid　complexing　method　coupled　with　ultrasonic　treatment.　We　characterized　the　materials　by　a　number　of　analytical　techniques.　It　was　found　that　the　NdSrCu1-xCoxO4-delta　and　Sm1.8Ce0.2Cu1-xCoxO4+delta　catalysts　possess　T　and　T　crystal　structures,　respectively.　There　are　Cu3+/Cu2+　ions　and　oxygen　vacancies　in　the　former　and　Cu2+/Cu+　ions　and　extra　(over-stoichiometric)　oxygen　in　the　latter.　We　examined　the　catalytic　activity　of　the　materials　for　methane　combustion.　Methane　conversion　increased　with　a　rise　in　the　amount　of　nonstoichiometric　oxygen　over　the　two　series　of　catalysts.　It　is　concluded　that　oxygen　nonstoichiometry　and　Cu3+/Cu2+　or　Cu2+/Cu+　redox　couples　facilitate　the　oxidation　of　methane　over　the　NdSrCu1-xCoxO4-delta　and　Sm1.8Ce0.2Cu1-xCoxO4+delta　catalysts.　(C)　2008　Elsevier　B.V.　All　rights　reserved.