Thermal stability of equidistant nanometer (nm) range Ti/Ni multilayer (ML) structures have been studied to investigate the interfacial microstructural changes upon thermal annealing. Two different ML having bilayer periodicity 10 nm, i.e., [Ti(5 nm)/Ni(5 nm)](10) and 6 nm, i.e., Ti (3 nm)Ni(3 nm)](10) were prepared under ultra high vacuum deposition condition. It was observed that when the bilayer periodicity is changed from 10 nm to 6 nm, the individual layers grow in an amorphous form as compared to poly-crystalline layers of the former. The X-ray diffraction measurements show significantly different changes in the structural properties of the two ML. Moreover, the interdiffusion measurements carried out on both the ML, using X-ray reflectivity technique indicates slower inter-diffusion in case of samples having smaller periodicity. The hysteresis measurements on a ML with 10 nm periodicity show a drastic change in the magnetization behavior of the sample when annealed at or above 300 degrees C. The observed magnetization behavior is explained on the basis of structural and chemical changes that have occurred at the interface due to the thermal treatment. (c) 2006 Elsevier B.V. All rights reserved.