Reversed micelle method was used to prepare mesoporous titania membranes. Three kinds of reversed micelle microemulsion containing different sizes of titania particles were prepared by using tetrabutyltitanate and water, and cyclohexane as solvent. span-80 as surfactant and iso-pentanol as accessory surfactant. Firstly, the surface tension method was used to determine the CMC (critical micelle concentration) of span-80 in cyclohexane. Secondly, the amount of iso-pentanol for maintaining the formation of reversed micelle microemulsion was measured by light permeance method. It was found that the titania particle size increased first when [H2O]/[span-80] increased from 13.9 to 55.5 and then decreased when [H2O]/[span-80] increased from 55.5 to 110.9 by TEM. which was confirmed by the pore size distributions of the unsupported membranes by BET (Brunauer, Emmett and Teller) method. The unsupported membrane prepared from the microemulsion with [H2O]/[span-80] of 110.9 had the narrowest pore size distribution, and its predominant pore size was about 4.5 nm. Therefore, the same microemulsion was used to prepare supported titania membrane. The prepared supported titania membrane had the prominent pore size of 16 rum by liquid-liquid displacement porometry (LLDP) method. The clean water permeability was 15.7 x 10(-5) m(3) m(-2) s(-1) MPa-1 and the single gas permeability of N-2 and H-2 were 4.3 and 14.1 mol m(-2) s(-1) MPa-1 at room temperature, respectively.