Oxidative coupling of methane was investigated on Na/CaO and Ce/Na/CaO catalysts with different sodium and cerium contents. The reaction was carried out in a micro fixed-bed flow reactor operating at atmospheric pressure, at 700 and 750 degrees C and molar ratio feed of CH4 : O-2 : N-2 = 50 : 10 : 40. Catalysts were compared at isoconversion and were characterized by BET, XRD and XPS. The addition of cerium to Na/CaO catalyst increased the specific activity by a factor of eight. These catalytic and characterization results were related to the presence not only of Na+O- active sites, formed by the introduction of Na+ in the CaO lattice, but also to peroxide active sites. A mechanism is proposed to explain the role of cerium in increasing the rate of the regeneration step of the O-s(-) and Na2O2 sites.