In this paper, the thermal study of a TiN/AlN superlattice was reported. The thermal stability of a superlattice structure and a crystal structure of cubic AlN in a TiN/AlN superlattice were evaluated by using in situ high temperature transmission electron microscopy (HTTEM), X-ray diffraction (XRD) measurements and TEM observations after an annealing treatment in a hydrogen atmosphere, and semi in situ high temperature X-ray diffraction (HTXRD) in a nitrogen atmosphere. It was confirmed that the superlattice structure remained up to 1473 K for a short time by HTTEM observation. HTXRD studies showed that the superlattice structure and c-AlN remained after 1273 K annealing for 3.5 h. According to the change of low angle diffraction intensity of HTXRD, two kinds of diffusion processes may operate. One was short range diffusion that improved the superlattice structure from 1073-1233 K and the other was long range diffusion that started at above 1233 K.