Organosilica membranes were developed and showed excellent stability in aqueous solutions, which raised expectation for applications to pervaporation dehydration. In order to investigate the properties of pervaporation through organosilica membranes, 1,2-(bistriethoxysilyl)ethane (BTESE)-derived membranes with different pore sizes (0.44 nm and 0.54 nm) were prepared by tuning the acid molar ratio in the sols, then applying the resultant membranes to the gas permeation of various single gases (He, H-2, CO2, N-2, CH4, CF4, and SP6) as well as to the pervaporation dehydration of aqueous solutions (methanol, ethanol, n-propanol, iso-propanol, n-butanol, tert-butanol, acetone, and n-methyl-2-pyrrolidone). Both membranes showed high levels of both water permeance ( > 10(-6) mol/(m(2) s Pa)) and separation factors for water/iso-propanol (500-6000). Both the permeances in pervaporation and in gas permeation tended to decrease with an increase in the molecular size and a decrease in the pore size, which confirmed the contribution of the molecular sieving effect. Pervaporation performance was correlated with gas permeation performance.