Expanding zeolite pore sizes beyond the microporous regime has long been limited by conventional organic structure-directing agents (OSDAs). Here we report JU-69, a mesoporous pure-silica zeolite that features one-dimensional 36-ring channels, representing the largest apertures (19.5 Å × 25.2 Å) observed in any known TO4-based zeolite framework and an ultralow framework density of 9.53 T per 1000 Å3 (T: tetrahedral framework atom). A surfactant-like phosphonium OSDA with bulky head groups and a long alkyl chain directs columnar assemblies that template long-range-ordered mesoporous walls. Three-dimensional electron diffraction reveals a trigonal framework built from three composite building units (CBUs), including cas and two previously unknown CBUs that generate chiral clover arrangements and circular 36-ring pores. The structure is further validated by atomic-resolution real-space imaging using electron ptychography. JU-69 exhibits thermal stability up to 900 °C and periodically arranged silanol groups that enable efficient metal anchoring, demonstrated by active Pd/JU-69 catalysts for bulky molecule hydrogenation. This work establishes a pathway for designing crystalline mesoporous zeolites with unprecedented structural openness.