Structural deformations and phase transformations of Rb-boroleucite RbBSi₂O₆ obtained by crystallization from glass at 1000 °C are studied by high-temperature X-ray powder diffraction and differential scanning calorimetry in the range 25–1200 °C. At 345 °C the compound undergoes a reversible cubic-cubic polymorphic transition with increasing symmetry I4 ¯ 3 d↔ Ia3 ¯ d. The crystal structure of RbBSi₂O₆ is refined by the Rietveld method at temperatures of 25 °C, 100 °C, 200 °C, 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 380 °C, 400 °C, 500 °C, 600 °C, 700 °C, 800 °C, and 900 °C, according to the powder X-ray diffraction data.