The phase relationships and electric conductivities of the ternary iodide systems LiI-MnI2 (Mn=Mn, Cd, Pb) have been studied by high-temperature X-ray measurements and impedance spectroscopy methods. Whereas mutual solubility of LiI and Mnl2 is negligible at any temperature deficient NaCl-type mixed crystals Lit_xM[~.nxI (MIX= Mn, Cd, Pb) are formed at temperature above 540 K, which, however, cannot be quenched to ambient temperature. The solid solutions obtained exhibit high ionic conductivity, e.g. 1 × 10-t, 3 × 10-2 and 7 × 10-2 f~-~ cm-~ at 570 K for materials like Li2CdI4, Li2Pbl4, and Li4PbI6, respectively.