To produce nitrogen-free synthesis gas or hydrogen by the partial oxidation of methane using air as ail oxidant, NiO-Cr2O3-MgO complex oxide was proposed as ail effective one. Lattice oxygen of NiO in the complex oxide was effectively transferred to CH4 to give H-2 and CO in the ratio of 2-3:1 at 700 degrees C. NiO was reduced to metallic Ni during the Course of the reaction with CH4, and the reduced Ni was successfully oxidized to NiO with air at 700 degrees C. Repeated cycles of the reaction and oxidation were carried out without any loss of activity. The role of Cr2O3 seemed to weaken the Ni-O bond in NiO-MgO complex oxide, in which NiO is less reducible with CH4 at 700 degrees C. In addition, the surface oxidation state of Ni was increased to Ni3+ with Cr2O3.