Ultra-thin dense zirconia/yttria membrane composites were fabricated by EVD technique on porous cu-alumina substrates. The deposited membranes consisted primarily of cubic/tetragonal phases as determined by XRD. The EVD film growth rate estimated by SEM photographs was 3-4 mu m/h. Oxygen permeation data of thin dense zirconia/yttria membranes with different thickness (2-15 mu m) were measured at 900 degrees C and 1000 degrees C. From the oxygen permeation data, the surface reaction and bulk diffusion rate parameters, alpha and beta, were calculated. At 900 degrees C, alpha = 3.0 x 10(-8) mol/cm(2).s.atm(1/2) and beta = 3.0 x 10(-8) mol/cm.s.atm(1/4) with activation energy 53 KJ/mol and 72 KJ/mol for alpha and beta, respectively. Presence of steam in the high oxygen partial pressure side promoted electrochemical surface reaction.