Thin film composite （TFC） membranes for the oxygen enrichment were prepared. Poly(dimethylsiloxane) was used as a coating material and polysulfone was utilized for a porous support membrane. The thickness of the coated layer was 4-6μm and that of the porous polysulfone support membrane was about 60μm. The permeabilities of oxygen, air and nitrogen increased linearly with the increase in the pressure difference (P_d) but the selectivity was independent of the pressure difference. The effects of the operating parameters (pressure ratio P_r and cut θ) on the air separation were investigated for the different mixtures of oxygen and nitrogen as the feed stream. The extent of the oxygen enrichment increased with the decrease of the pressure ratio and cut. Oxygen was enriched upto 28 % in the permeate stream under the condition such that the values of pressure ratio, cut and oxygen mole fraction in the feed stream were 0.171, 0.01 and 0.21 respectively. The ideal separation factor (α^*) of this TFC membrane was 2.03 and the permeability of oxygen was 1.1×10^-4[cm³(STP)/cm³·sec·cmHg].