Positron techniques provide a non-destructive method to study open volumes, surface area and porosity inside molecular media. The techniques are also considered from the rare insitu tools which can probe the changes of the material properties in the time of measurements. Positron annihilation lifetime spectroscopy (PALS) may be uniquely capable of deducing a pore size, pore size distribution and the degree of filling of the pores in closed pore systems (not interconnected). In this particular case, the gas adsorption techniques are not applicable. This thesis has two main goals. Firstly and for the first time, the positron annihilation lifetime technique is used to characterize the control porous glasses (CPGs) media (from 1 nm to 64 nm). The PALS is used to establish basic correlations between the important physical properties of the CPG (pore size, surface area, and porosity) and the o-Ps lifetime. These correlations can be used as calibration curves in characterization of mesoporous glasses by the interested research groups. Hence, the PAL technique will be more precise and more time saving than the other tools such as gas adsorption-desorption and Hg mercury intrusion porosimetry. The second goal is to use these correlations to verify the validity of some suggested models (RTE- and ETE-models) and theories to discover possible deviations from the expected behaviour and to discuss the physical point of view for these deviations.