Abstract: This article presents the results of determining the crack resistance of quartzoid glasses (QGs) doped with cesium. Crack resistance is calculated on the basis of measured values of microhardness and Young’s modulus. The relationship of crack resistance with the content of cesium oxide (Cs2O 0.76–2.11 wt %) in glass is analyzed. The results of measuring 11B and 29Si NMR spectra are used to interpret the effect of the presence of cesium in glass on the ability of the studied material to resist crack formation.