An order-disorder phase transition is found in a hexafluorosilicate-based crystal, bis(betainium) hexafluorosilicate bis (betaine) (1). At room temperature, 1 crystallizes in an orthorhombic space group Fddd and the hexafluorosilicate moiety exhibits partial disorder which originates from a uniaxial wheellike rotation. As temperature decreases, a total freeze of this wheel-like motion results in a second-order phase transition at 250 K and the low temperature phase of 1 belongs to a monoclinic space group C/2c. Thermal measurements and variable-temperature single-crystal X-ray diffractions confirm that distinctive order-disorder transformation of the anionic rotor is the main driving force for the solid-state phase transition. Further, theoretical computation of potential energies for the wheel-like motion elucidates the dynamic changes in the anion from rotating to static state. Moreover, dynamic changes of the crystalline in-plane rotor give rise to anisotropic and switchable dielectric constants.[a] S.