Oxidative coupling of methane (OCM) was studied on strontium titanate perovskite oxides whose A site ion (Sr 2+ ) was partly substituted by various metal ions. The pulse reaction of methane with oxides gave either C2 hydrocarbons (C2) or carbon oxides (CO x ). When Sr 2+ in SrTiO3 was substituted by Ca 2+ , its activity and selectivity for producing C2 decreased whereas when the Sr 2+ was substituted by Mg 2+ its activity for C2 formation was promoted. Substitution of Sr 2+ by Mg 2+ (especially, when the substitution was 0.04-0.10), it especially promoted the catalytic activity of OCM while its chemical character (basicity) was unchanged. Substitution by Mg 2+ reduced the crystal size and strain in the crystallite and promoted the specific surface area. At 4% substitution, the crystallite size was minimum and the catalytic function was maximum. It was concluded that the introduction of Mg 2+ suppressed the crystal growth while maintaining the perovskite structure provided a larger surface area and that the promotion of catalytic activity was attributed to the increased number of active sites stemming from the larger surface area.