The thermodynamical data of solid and gaseous aluminium neodymium chloride have been obtained by determination of the decomposition equilibria (of solid) from total pressure measurements and chemical transport reactions (gaseous). The melting diagram was determined by DTA. The enthalpy of formation of the solid phase was calculated from their heats of solution and from the enthalpies of formation and the heats of solution of NdCl 3 and AlCl 3 . Data by total pressure measurement: ΔH° B |(NdAl 3 Cl 12,f,298 ) = -749,6 ± 2,5 kcal/mol; S°(NdAl 3 Cl 12,f,298 ) = 118,2 ± 3,0 cal/K·mol. Data by solution calorimetry: ΔH° B (NdAl 3 Cl 12,f,298 ) = -748,6 ± 1,3 kcal/mol. Data by chemical transport: ΔH° B (NdAl 3 Cl 12,g,298 ) = -701,5 ± 3,0 kcal/mol; S°(NdAl 3 Cl 12,g,298 ) = 215,0 ± 4,0 cal/K-mol.