Applying Rietveld's profile refinement method to the neutron powder diffraction patterns, the structures and orientations of the nitrate group in RbNO3 are determined. Phase III (437 to 492 K) has cubic CsCl‐structure, Pm3m, with one molecule per unit cell. The structural analysis gives a slight preference to the twelve‐orientations model for rigid NO 3−. Phase II (492 to 557 K) has rhombohedral unit cell with space group R3m, phase I (557 to 583 K) cubic NaCl‐type unit cell, Fm3m, with four molecules per unit cell. In both of these phases the aragonite type of disorder for the rigid nitrate group is proposed.