Plasma Polymerization of three organosilicon compounds, hexamethyldisiloxane (M,2,), hexamethylcyclotrisiloxane (D,3,), octamethylcyclotetrasiloxane(D,1,), were carried out in a capacitively coupled tuber reactor with external electrodes. Polymers were deposited on the porous polypropylene substrase. Gas permeability of these composite membranes were studied. These composite membranes showed high oxygen permeabitity of 3.7—15×10,-9, cm,3, (STP)/cm,2,•s• Pa. The composite membrane prepared from M,2, showed the highest oxygen/nitrogen separation factor of 3.1. The deposited films were investigated by IR, XPS and SEM.