Polysufone (PSf) hollow fibre membranes with high gas separation performance were prepared from N-methyl-2-pyrrolidone (NMP)/H2O and NMP/ethanol solvent systems. Water was used as the external coagulant. The internal coagulants used include water, ethanol, 2-propanol, the mixture of water/ethanol and water/2-propanol. The effect of air gaps, the polymer concentration and the coagulation bath temperature on the membrane structure and gas permeation properties was investigated. The membranes were characterized by measuring their gas permeation properties for He, CO2, O-2 and N-2 and by examining cross-sectional structures using scanning electron microscopy (SEM). A dilute silicone coating method was used to seal defects on the outer surface of the hollow fibres. The silicone-coated hollow fibres exhibit O-2 Permeance of 20-30 GPU and O-2/N-2 selectivity of 5-6.5 at 25 degreesC. Apparent separating layer thickness determined by the gas permeation is in the range of 370-500 Angstrom.