Abstract: The crystal structure and thermal behavior of Rb3SO4F a new compound is studied by in situ single-crystal X-ray diffraction analysis in a wide temperature range. The compound is stable up to a temperature of 377(10)°C and does not undergo phase transitions during heating. Calculation of the coefficients of the thermal expansion tensor showed that the structure expands strongly anisotropically: the maximum thermal expansion is observed in the ab plane, while the minimum is parallel to the [001] direction, which is closely correlated to changes in bond lengths and angles in the anion-centered FRb6 octahedron.