The phase diagrams of the ACl/YbCl3 (A=Cs,Rb,K) systems were investigated by DTA and XRD. Compounds A(3)YbCl(6), A(2)YbCl(5) and AYb(2)Cl(7) exist in all systems, enneachlorides A(3)Yb(2)C(4) in the systems with A=Cs,K. In the group AYb(2)Cl(7), the Yb ions have coordination number 7, in all other compounds the coordination is octahedral. Thermodynamic functions determined by solution calorimetry and emf vs T measurements in galvanic cells for solid electrolytes reveal that the ternary chlorides A(n)YbCl(3+n) an stable compared with mixtures (nACl+YbCl3); the compounds Cs2YbCl5 and Rb2YbCl5 are stable only at temperatures >0 K.