Knowledge of the mechanical properties of glass and ceramic surfaces is important in terms of friction, wear, strength, etc. In particular, understanding and controlling the mechanical properties of the mesoscale near the surface is essential to improve the mechanical reliability of glasses and ceramics as a result of chemical changes caused by the external environment. Bending tests using microcantilever specimens are an excellent method for pinpointing any point in a material. The objective of this study was to investigate the effects of chemical reactions on glass and ceramic surfaces and their influence on the mechanical properties of the near-surface region. In soda-lime glass produced by the float method, SO2 gas is blown onto its surface, changing its composition by several tens of nm. It was found that the fracture toughness near the surface is improved by removing this region by etching. Such degradation due to chemical reactions occurred similarly in silicon nitride ceramics containing a grain boundary glass phase, and it is clear that immersion in molten Al or sulfuric acid causes degradation of the mechanical properties of the grain boundaries. On the other hand, in aluminosilicate glass, replacing Na⁺ with K⁺ resulted in a significant increase in strength, although the fracture toughness remained unchanged. Since the specimen height was smaller than the compressive stress layer in this test, it was concluded that the mechanical properties were evaluated only in the chemically altered region, and the higher strength was attributed to the increase in Young's modulus resulting from ion exchange. In addition, when microcantilever specimens fabricated on quartz glass were subjected to bending tests in water, their strength was higher than that measured in air. This may be attributed to the volumetric expansion due to the diffusion of water near the surface of the quartz glass as a result of the high tensile stress. In conclusion, the proper use of chemical reactions in glass and ceramics can contribute significantly to improving their mechanical properties and mechanical reliability.