This paper reports preparation and properties of ultra-thin MFI-type zeolite (silicalite) films on sol-gel derived mesoporous 8 mol% yttria doped zirconia (YZ) supports by the in situ synthesis method. Only non-continuous zeolite films were obtained on the as-synthesized YZ supports (calcined at 450 degrees C). Continuous polycrystalline pure silicalite films, with a thickness of 0.5-0.7 mu m, could be grown on the YZ supports pretreated at 700 degrees C. The difference in the oxygen vacancy defect concentrations in these two types of YZ supports is suggested to explain the different results of growing silicalite films. Moreover, defect free 2-3 mu m thick silicalite films were also prepared on the alpha-alumina supports under the same synthesis conditions. The silicalite layer on the YZ support offers a significantly lower mass transfer resistance as compared to that on the alumina support. Single gas permeation data of hydrogen, methane and ethane through these membranes were measured and compared with those of silicalite membranes prepared by other groups. The alumina supported silicalite membranes prepared in this work show better separation factors than the literature values. The zeolite film on the YZ support is less resistant to the stress induced in the step of template removal as compared to the zeolite film on the alumina support.