In this work Silicalite-1 films were prepared on porous ?-alumina micro filtration filters acting as a support using the ”seed film method”. The films were modified using an aqueous solution of Ca(NO3)2 in order to obtain a carbon dioxide (CO2) selective membrane. Two different modification procedures were developed in the present work. The procedures are denoted “evacuation” and “spinning technique”. Single gas permeation and n-hexane porosimetry were used for the characterisation of the membranes. CO2, nitrogen (N2), helium (He) and hydrogen (H2) were used as probe molecules in single gas permeation experiments. n-Hexane porosimetry was used to determine the amount of defects in the membranes. Both modified and unmodified samples were characterized using these techniques. It was found that a high concentration of Ca(NO3)2 deteriorated the membrane quality according to porosimetry data. The CO2/(H2, N2 or He) permeance ratios became slightly higher after modification of samples modified with a lower salt concentration. However, no significant difference between the two modified methods could be observed with respect to CO2 selectivity. It may be thus concluded that CaO was not optimally deposited in the silicalite-1 film. EDS and SEM analysis showed the concentration of Ca varied on the surface but was distributed without aggregates.