It was found that methane was selectively oxidized by water molecule to give C2 hydrocarbons and hydrogen at high temperature (>750°C) on perovskite type oxide such as strontium titanate whose titanate ions are partly substituted by Mg2+ ions. C2 hydrocabons were formed only when water was fed with methane whereas catalysts were reduced in the absence of water. The activity and the selectivity of C2 hydrocarbon formation on SrTi0.4Mg0.6O3 δ were much higher than those on SrTiO3. This was the same to other provskite oxides. This suggested that the oxidative coupling of methane by water promoted formation of oxide ion defects.