${gamma}-alumina$ membranes were prepared by sol-gel dip coating or pressurized coating of boehmite sols on slipcasted ${gamma}-alumina$ support tubes. The particle size of sols synthesized via the modified Yoldas-method could be controlled below 5 mn according to the mole ratio of nitric acid/aluminumtri-sec-butoxide (0.07~1.0). The reproducible crack-free composite membranes were produced by the 2nd dip coating or the pressurized coating technique using very stable sols with the particle size of 45 nm. Nitrogen gas permeability through the top-layer in the composite membrane was about $70~55{ imes}10^{-7};mol/m^2{cdot}s{cdot}Pa$. The thermal stability of the top layer was proved to be good enough upto the heat-treatment temperature of $500^{circ}C$.