A dry process for mutual separation of rare earths was investigated on a mixed oxide of praseodymium and neodymium using a flow-type chemical vapor transport reaction mediated by metal halide vapor complexes, KRCl(4)(g) (R = Pr, Nd). Some potassium salts, K2CO3, K2SO4, KNO3, KF, and KAl(SO4)(2), were used as a precursor of a complex former, KCl, and the yields of RCl(3) transported were 55, 37, 32, 18, and 26%, respectively, while the yield when the KCI was directly used as the complex former was 25%. The transport reactions using K2CO3 were carried out under various kinds of temperature gradients with a constant-temperature plateau zone, and the decrease of the temperature for such a plateau zone resulted in an increase of the separation factor for Nd. Empirical vapor pressures of KPrCl4(g) and KNdCl4(g) as a function of temperature were evaluated by altering the plateau temperature. The empirical vapor pressures were about 1 order smaller than those expected from the existing thermodynamical functions probably due to a nonequilibrium flow-type reaction in this system. Finally, a heat necessary for the chemical vapor transport of Nd2O3 using K2CO3 as the precursor was calculated as 191.2 kJ mol(-1) of Nd.