Oxygen enriching property and stability of the blend membranes, 10-45μm thick, fabricated from ethyl cellulose, cellulose nitrate, cellulose diacetate, and cellulose triacetate, with thermotropic cholesteric or nematic liquid crystals (LC), such as cholesteryl oleyl carbonate, p-heptyl-p'-cyanobiphenyl, p-pentylphenol-p'-methoxybenzoate, benzoate-containing liquid crystal mixture, and triheptyl cellulose, were studied by a variable volume method. The membranes with 1.5-4 wt% LCs showed the maximum oxygen-enriching ability in the temperature range of their LC phase. The oxygen-enriched air flux Q O E A and the oxygen concentration Y O 2 increased simultaneously as the operating pressure increased. The 30μm-thick triheptyl cellulose/ethyl cellulose (8/92) homogeneous membrane exhibited almost constant oxygen- enriching efficiencies of Q O E A 1.0x10 - 4 ml(STP)/s.cm 2 and Y O 2 40% at 30 o C and 0.41 MPa in a single step for a 35 day operating time.