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It is difficult to control the heterogeneous nucleation and growth of crystals on porous supports, the preparation of thin ZIF-8 membranes is still extremely challenging. Herein, a two-dimensional transformation strategy is demonstrated for constructing a ZIF-8/GO 'sandwich' composite membrane with a thickness of ∼0.9 μm, which was prepared from Zn-EG-AC (EG: ethylene glycol, AC: CH 3 COO-groups, abbreviated as ZnEG) on alumina hollow fiber support for the first time by precursor conversion method in 2-methylimidazole methanol solution. The effects of the amount of precursor, reaction time and membrane thickness on the membrane structure and H 2 /CO 2 separation performance are explored. The sieving effect of ZIF-8 and the adsorption effect of 2-methylimidazole rings on CO 2 , as well as the strong interaction between GO and CO 2 hinder the permeation of CO 2 into the membrane, thus exhibiting a good H 2 /CO 2 ideal separation selectivity of 30.8 with the H 2 permeance of 1.36 × 10−7 mol·Pa−1·m−2·s−1 under the optimized preparation conditions. The separation factor of the equimolar H 2 /CO 2 binary-mixture gases stabilizes to ∼25 after 30 h. This precursor conversion strategy is expected to be extended to other MOF/graphene oxide (GO) composite membrane systems. Thin ZIF-8/GO sandwich composite membranes can be obtained on alumina hollow fiber supports by a precursor conversion strategy. [Display omitted] • Thin ZIF-8/GO sandwich composite membranes on alumina hollow fibers. • Zinc glycol/GO precursors to ZIF-8/GO membranes by precursor conversion. • The thickness of the high quality ZIF-8/GO membrane is only 0.9 μm. • ZIF-8/GO membranes have considerable H 2 /CO 2 separation selectivity. [ABSTRACT FROM AUTHOR]