Participation of F+ centers with the formation of superbase sites was studied, Two kinds of ESR signals were observed with Na metal doped MgO, which was thermally activated at 773, 873, and 973 K. A relationship was found between double bond migration activity of 3-methyl-1-butene and ESR signal intensity which was observed at low magnetic field. This radical species was assigned to an F+ center formed on an unstable MgO surface. The maximum activity was obtained when two electrons were trapped in an anion vacancy. It was concluded that the F+ and F centers played the most important role for the formation of superbase sites.