We report the results of thermal stability study carried out on C/B4C multilayer structure. We have analyzed the structure of as-deposited and vacuum annealed C/B4C multilayer film by soft X-ray reflectivity measurements. We observed that multilayer period expansion continues till 600 degrees C and slight contraction at higher annealing temperature. The results show that the multilayer structure is stable even after 700 degrees C annealing. Raman spectroscopy indicates graphitization of carbon layerwith increasing annealing temperature. Graphitization of carbon results in increases of layer thickness and decreases in density as also observed by soft X-ray reflectivity. We observed reduction in measured soft X-ray reflectivity at 6.56 and 4.39 nm wavelengths after 800 degrees C annealing. C/B4C multilayer structure has been tested over a period of one year to investigate its temporal stability. (C) 2012 Elsevier B. V. All rights reserved.