The calculation of the ultimate strength of the silicate glasses, based on the microheterogeneous structure of these systems, is presented. The ultimate strength is determined by the stress ( δ n = − U o / r 3 o ) required for certain configurational changes (quasi-breaking, local loosening) in the glass structure at the boundaries between the microheterogeneities (microblocks, complexes). The ultimate strength depends not only on the modulus of elasticity E = β/ r o , where β is the power factor, but also on Poisson's ratio μ, which depends, together withβ, on the disharmony of the bonds g. It is shown that the disharmony of the bonds plays an important role in certain cases in the process of the glass destruction (fracture). The interrelationship between the ultimate strength and microhardness, surface tension, thermal expansion coefficient, glass-transition temperature, internal molecular pressure, which all depend on the same, in nature, configurational changes of the structure in the boundary region, as those of the destruction, are presented.