The utilization of W/B4C multilayer structures as Bragg diffractors rests in their reflective efficiency and dependability, both of which rely on the stability of the layered structure. The layers within the vapor deposited multilayers, often amorphous, are typically metastable, hence susceptible to thermally induced structural change. In fact, crystallization and compound formation are known to occur in annealed multilayer systems. In this study, multilayers of W/C and W/B4C were vacuum heat treated, then structurally examined. A comparison between the pre- and post- heat treated structures of the two multilayer systems, accomplished using diffraction and electron microscopy, indicate structural stability in the W/B4C multilayers as opposed to structural degradation noted for the W/C system.