ZnO added to a NaOH-CaO catalyst by the incipient wetness method affects C-2 hydrocarbon selectivity in the oxidative coupling of methane. The zinc content was varied between 0.0001 and 1 mol-%. At concentrations from 0.0001 to 0.05 mol-% an increase in selectivity was observed as compared to the undoped catalysts. By X-ray photoelectron spectroscopy analysis of the catalyst surface a negative shift in binding energy of the Zn 2p(3/2) peak in the range of enhanced selectivity was observed which is ascribed to an incorporation of zinc cations into the CaO surface lattice. The selectivity increase is supposed to be due to Zn2+ accepting electrons from CH3- formed by heterolytic splitting of methane and the subsequent reduction of adsorbed oxygen to O-2 lattice oxygen by electron transfer from Zn1+ or Zn-0.