We studied solid state reactions of magnesium oxide/titanium oxide ceramics superlattice thin films in the air in the temperature range from 525 to 600°C by using X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Two different kinds of solid state reactions took place at the interface and on the surface. The periodicity of the superlattice, of about 6nm, increased monotonously depending on the annealing time. The change was caused by the homogeneous interfacial reaction between magnesium oxide layer and titanium oxide layer resulting in the growth of inverse spinel crystals (Mg₂TiO₄). Simultaneously with this process, spinel crystals (Mg₂TiO₄ or MgTi₂O₄) were formed as distinctly shown by XRD. It was clarified by HRTEM that these spinels were formed on the surface of the films. The growth rate of the spinel crystals obeyed a parabolic equation. We confirmed that the surface reaction rate was murh hitcher than the interfacial reaction rate.