Mixed matrix membranes (MMMs) have attracted tremendous attention in the field of gas separation, which adopts the synergistic advantages of the polymer and inorganic phase. However, the MMMs rarely generate sufficient selectivity for energy-efficient gas separation, even if the dispersed molecular sieve is highly selective. Here, an unprecedented improvement (similar to 4.5-fold) of both C3H6/C3H8 permeability and selectivity on the crosslinked poly(ethylene oxide) (XLPEO) membranes containing ZIF-8 nanocrystals. When the ratio of polymer-to-sieve permeability (R-c/d) is in the range of 0.004-0.36, both C3H6/C3H8 permeability and selectivity increases with the ZIF-8 loading, and the separation performance on MMMs can approach and surpass the-state-of-the-art polymer upper bound. Besides C3H6/C3H8 separation, the universality of this proposed polymer-sieve matching law is suitable for other gas-pairs on MOF-based MMMs. (C) 2019 Elsevier Ltd. All rights reserved.