The effect of nanosized particles of ZrO2 and Al2O3 on physicomechanical properties (elastic modulus, flexural strength, microhardness), phase composition, and also the microstructure of materials based on Si-B4C-ZrB2 is studied. After heat treatment in air in an electric furnace, a borosilicate glass-forming melt was obtained by a reaction method, which had an encapsulating effect on the starting components. As a result, gradient glassceramic materials were obtained in which the surface glass-ceramic layer protects the underlying layers from oxidation. This approach can be used to obtain protective coatings for carbon materials. It is shown that the introduced additives improve the mechanical properties of the composites.