Adsorptive separation of propylene (C 3 H 6 ) from propane (C 3 H 8 ), which could deal with energy-intensive cryogenic distillation technologies, remains challenging due to their similar physiochemical properties. Herein, we present a pure silica zeolite with ordered silanols (OSs), whose crystallographic structure was unraveled by the advanced three-dimensional electron diffraction (3D ED), displaying the highly efficient separation of propylene from propane under ambient conditions. The 3D ED technique enables us to investigate its 8-ring pore opening transformation from the round one to the elliptical one during the removal of organic structure-directing agents. Such unique elliptical 8-ring pore openings can exclude larger-size propane and only adsorb propylene. Its C 3 H 6 /C 3 H 8 separation performance is also confirmed by column breakthrough experiments, showing a high dynamic adsorption capacity of 53.36 cm 3 g -1 for C 3 H 6 but negligible C 3 H 8 under ambient conditions. The dynamic capacity for C 3 H 6 is superior to that of the well-known pure silica DDR -type zeolite (31.07 cm 3 g -1 ). The density functional theory calculation demonstrates that the adsorbed propylene is distributed in the heart-shaped cavity and has a weak interaction with the OSs.