The membrane separation process has bee considered as an alternative to conventional processes due to its energy savings and low capital costs. Mixed matrix membranes (MMMs) have bee developed and tested for both gas and liquid separations over the last few decades. In this work, solid-polymer and solid-liquid-polymer MMMs were developed and investigated for CO2/N2, CO2/H2 and C3H6/C3H8 separations using pure gas measurements at room temperature as well as for plasticization phenomenon. Activated carbon (Act.C), polyethylene glycol (PEG), silicone rubber (SIR), and polysulfone (PS) were used as solid, liquid, polymer phases, and a support, respectively. The Act.C/SIR/PS MMM enhanced CO2/N2 selectivity significantly but only slightly for CO2/H2 and C3H6/C3H8 selectivities if the PEG was suspended in the polymer phase; however, this resulted in a decrease in permeability. For the plasticization phenomenon, only 30wt% Act.C/SIR/PS MMM had a strong hydrostatic compression effect at low pressures. Plasticization effect of C3H8, C3H6 and CO2 decreased with increasing amount of PEG