The phase diagrams of the binary system KBF4-K2TiF6 and of the ternary system KF-KBF4-K2TiF6 were determined using the thermal analysis method. The subsequent coupled analysis of the thermodynamic and phase diagram data was performed to obtain a thermodynamically consistent phase diagram. In the system KF-KBF4-K2TiF6, the intermediate compound K3TiF7 is formed. The K3TiF7-KBF4 joint divides the ternary system into two simple eutectic ones. The calculated coordinates of the two ternary eutectic points are : e(1) : 26 mol% KF, 69 mol% KBF4, 5 mol% K2TiF6, t(e1) = 448 degrees C; and e(2) : 4 mol% KF, 69 mol% KBF4, 27 mol% K2TiF6, t(e2) = 440 degrees C. The system KBF4-K2TiF6 is a simple eutectic one with the calculated coordinates of the eutectic point being 28 mol% K2TiF6 and 448 degrees C. The probable inaccuracy in the calculated ternary phase diagram is 11.5 degrees C.