AbstractHigh silica zeolite ZK‐5 (framework Si/Al=4.8) has been prepared by interzeolite conversion from ultrastable zeolite Y via a co‐templating route using alkali metal cations and nitrate anions but without organic structure directing agents. The mechanism, which involves zeolite framework – alkali metal cation – nitrate anion ordering, has been established by a combination of chemical and thermal analyses, Raman spectroscopy, computational modelling, and X‐ray powder diffraction. Ammonium exchange gives ZK‐5 with occluded ammonium nitrate and subsequent heating gives microporous zeolite ZK‐5.