CsCl-NdCl3 is the next of binary MCI-NdCl3 systems (M: alkali metal) investigated for determination of relative internal mobilities of cations (b(Cs), b(Nd)) by countercurrent electromigration method (Klemm's method). The results have been presented as isotherms of internal mobilities of Cs+ and Nd3+ ions on NdCl3 equivalent fraction (y(Nd)). It has been found that internal mobility of cesium cations is higher than neodymium ones in the entire composition range (what is typical for nonsymmetrical MCI-LnCl(3) systems (M: Li, Na, K; Ln: La, Nd, Dy)) and decreases with increase of NdCl3 concentration in the melt. Generally, dependence of internal mobility of lanthanide cations in melts with alkali metal chlorides on lanthanide (i.e. its atomic number and concentration) seems strongly related to stability of chloride complex anions of lanthanides in the melt. Investigated systems may be divided into two classes. The first class includes MCI-NdCl3 systems (M: Li, Na) characterized by decrease of b(Nd) with increase of NdCl3 concentration. The second includes KCI-LnCl(3) systems (Ln: La, Nd, Dy) and presented here CsCl-NdCl3 system, and is characterized by increase of b(Ln) with concentration of Ln(3+) cation. The dependence of b(Nd) on NdCl3 concentration at 1073 K was fitted (as for other systems) by a simple equation of the form: b(Ln) = b(Ln)(0) + a(1 - y(LnCl3))(2), where b(Ln)(0) is the internal mobility of Ln(3+) cations in pure molten LnCl(3), a the difference between internal mobility of Ln(3+) cations in pure molten LnCl(3) and infinitely diluted LnCl(3) in molten alkali metal chloride (extrapolated), and y(LnCl3) is the equivalent fraction of LnCl(3). (C) 2010 Elsevier Ltd. All rights reserved.