Polysulfone is commonly used as the polymer matrix for designing new mixed matrix membranes (MMM), in this case by physical blending with com-patible inorganic fillers as polyhedral oligomericsilsesquioxanes (POSS). The reason polysulfone was chosen as polymer matrix is its superior chemical and thermal stability. These characteristics are attributed to its special structure, the iterative phenylene rings supplies an inflexible backbone which is resistant up against molecule rotation and keep molecule immobility. The polysulfone is one of the most used polymer matrix for the separation of CO2 as it is absorbed par-ticularly into the polymer matrix. The major enhancement in membrane technol-ogy is represented by the addition of inorganic materials in polymer matrix to form MMMs. This can enhance the permeability of CO2 while maintaining a high selectivity towards CO2 gas. The addition of inorganic fillers into polymer matrix has a relevant effect on the MMM’s gas separation performance as it is capable to modify the gas transport properties through the membrane. Emerging inorganic fillers such as POSS have been investigated in many fields of engi-neering and science and it was proved that they enhance the gas transport prop-erties of MMMs. POSS possesses unique cage structure and nano-scale diameter. POSS is a hybrid of inorganic and organic composition, Rn(SiO1.5)n where the R group can be from a wide range of the organofunctional group. It has a size of 1-3 nm which is the smallest possible silica particles. Because of the organic group attached to the POSS cage, it can be simple incorporated into a polymer matrix. The organic group provides resin compatibility whereas the various func-tionalities on POSS can be used to bind on various fillers to form nanomaterials. MMMs have some limitations. The agglomeration of nanofillers in the polymer matrix seems to be abig challenge faced in the fabrication of MMMs. Due to the small size of nanoparticles; they usually have high surface activity. The particles tend to concentrate and form aggregates. Because of the agglomeration of fillers, some defects are made in the MMMlike large pores and macro-voids which can-not be reached by polymer segments. These defects in the polymer matrix would degrade the gas separation performance. The interface compatibility between the polymer and inorganic filler determine the success of MMMs preparation. The adhesion problem at the polymer/filler interface results in voids formation which change in a negatively way the performance of gas separation as gas molecules could pass through the voids, making MMMs less selective. The objective of this research was to study the effect of the POSS’s introduction in the polysulfone matrix in order to use its in environmental applications.