Periodic multilayer Sb/B$_{4}$C composition with amorphous 2.59 nm-thick antimony layers and 1.81 nm-thick B$_{4}$C layers, which is a promising coating for X-ray optics, is made and characterized. Structure changes of the composition under heating up to 360°C are investigated using X-ray diffractometry and electron microscopy. As found, the thin Sb layers remain in the amorphous state in the multilayer Sb/B$_{4}$C composition up to 250°C. At a temperature of 290C, the antimony layers are crystallized. This leads to increasing of density of the antimony layers and to reduction of multilayer composition period by 13.8%. The antimony crystallization is accompanied by the formation of antimony lenses, which distort and destroy the multilayer coating.