The influence of various types of postsynthetic activations (calcination, treatment in neutral, acid and alkaline water mediums at 100°С, in hydrofluoric acid) on the state of silanol coverage of mesostructured silicated material MCM-41 surface was studied. The surface was characterized by XRD, IR-spectroscopy, thermogravimetric analysis and nitrogen adsorption. Activation of surface resulted in increasing silanol groups concentration. There was found the limit of the silanol number for МСМ-41, beyond which the material destruction caused because of structure features. The value of critical silanol number is 3-4 OH/nm2 for water solutions at 100°С. In spite of a destruction the specific characteristics of a material (the internal surface, volume, parameter of a lattice) remain invariable. Thus, there are limits on activation of a surface. The composition of reaction solution influences the rate of material collapse, but does not influence density of silanol coverage.