Phase diagram of the system AlF3-RbF was investigated by the methods of DTA, DSC and XRD with quenching technique. Three compounds were identified : Rb3AlF6; RbAlF4 and RbF . 3AlF(3). Rb3AlF6 melts congruently at 878 degrees C and alpha reversible arrow beta transforms reversibly at 340 degrees C. Eutectic E-l between Rb3AlF6 and RbF is located in 10.0 mol% AlF3 at 729 degrees C. RbF . 3AlF(3) melts incongruently at 745 degrees C, reacting with Rb3AlF6, second eutectic E-2 was observed in 48.4 mol% AlF3 at 486 degrees C. The third compound RbAlF4 was formed in the solid eutectic when it cooled below 473 degrees C. A very small thermal effect corresponding to alpha reversible arrow beta transformation at 335 degrees C was observed on the DTA curve of this compound. All phase structures in the system were confirmed by X-ray powder diffraction analysis.