The efficiency of glass utilization significantly decreases due to its low mechanical strength. For example, the loss of sheet glass during the stages of transportation and storage is 10-20 %, in some cases, reaching even higher values. The simplest method of improving the surface properties of glass is the thermochemical treatment of glassware by gas reagents. The aim of the undertaken experiments was to investigate the effect of thermochemical treatment by fluorine- and chlorine-containing reagents on mechanical strength of sheet glass. The subjects of investigation were flat glass samples. The chemical composition of glass is the following (weight %): 72.45 SiO2, 1.48 Al2O3, 0.11 Fe2O3, 7.72 CaO, 3.79 MgO, 13.71 Na2O, 0.34 K2O and 0.32 SO3. Such gas reagents as difluorodichloromethane and difluorochloromethane were used. Experiments were held in laboratory and industrial conditions. The following regime of glass treatment in laboratory conditions was used: temperature – 600 0C, duration – 15 min, quantity of gas reagent fed into the camera – 1.00 mol. Thermochemical treatment in industrial conditions was the following: temperature – between 600 and 950 0C, duration – between 10 and 20 min. Flow rate of reagent varied from 0.1 to 5.0 dm3/min. The mechanical strength of glass surface was determined by the method of central symmetrical flexure. The loading speed was 20 mm/min, using the press UMM-5. The number of samples used for testing in one experiment was not less then 100. The absolute error of measuring was ±20 MPa. The results were subjected to statistical analysis. Differential and integral curves of strength distribution of sheet glass for various regimes of thermochemical treatment have been made. There has been revealed a disparity in the strength levels of glass without treatment and of the samples, subjected to thermochemical treatment. The results show that the values of the strength of sheet glass are grouped around five levels: 60-70, 100-110, 145-160, 260-290 and 340-360 MPa. The untreated glass clearly shows the strength levels of 100, 145 and 260 MPa, while the levels of 60 and 340 MPa are mild. After thermochemical treatment the strength level of 60 MPa slightly shifted to 70 MPa and 95 MPa level - to 110 MPa. The dealkalized glass with the strength level of 260 MPa shifts to 300 MPa. Changes in the composition and structure of the surface layer of sheet glass under the influence of difluorodichloromethane and difluorochloromethane are characterized by the formation of a pronounced level of strength of 350 MPa. The obtained results show that the surface defects have a smaller influence on the strength of the dealcalized glass. Dealkalization of sheet glass by difluorodichloromethane and difluorochloromethane increases its minimum strength by 1.5 times. The mechanism of strengthening sheet glass, subjected to thermochemical treatment by fluorineand chlorine-containing reagents is discussed.