gamma Al2O3 membranes with highly tailorable pore sizes in the range of 50-60 Angstrom could be prepared by using surfactant micelles of varying sizes as templates. Surfactants were incorporated in the alumina sol by dissolving them in water above their critical micellar concentration and using the micellar solutions to hydrolyze aluminium alkoxides. 15 mM solutions of quaternary ammonium surfactants namely dodecyl trimethyl ammonium bromide, tetradecyl trimethyl ammonium bromide, and hexadecyl trimethyl ammonium bromide were found to give pore sizes of 50, 55 and 60 Angstrom respectively as obtained by nitrogen adsorption BET and transmission electron microscopy (TEM) methods. These pore sizes also match closely with the micellar sizes obtained by quasi elastic light scattering measurements. Moreover, it was also found that the total pore volume increases with increase of the amount of surfactant. Rejection of standard polyethylene glycol (PEG) solutions of different molecular weights as well as some globular protein solutions of different molecular weights was determined in these membranes and the data were explained on the basis of the model originally developed by Sourirajan and Matsuura and later modified by Brites and de Pinho.