A Knudsen cell mass spectrometric technique was used to study both the neutral and charged species that are in equilibrium in saturated vapor over lutetium trichloride. It was found that in the temperature range between 885 and 1100 K the vapor is comprised of molecular (LuCl 3 ) n and ionic Cl -(LuCl 3 ) n clusters where n = 1 -6. For neutral constituents, monomer and dimer molecules are the most abundant, the partial pressure of Lu 2 Cl 6 being about 22 per cent with regard to the total pressure at 1000 K. According to thermodynamic calculations dimer molecules become the dominant species of the equilibrium vapor above 1200 K. In the temperature range studied, the temperature dependencies of partial vapor pressures (atm) of monomer, dimer, trimer and tetramer molecules are approximated by the following equations ln P(LuCl 3 ) = (-31.4 ± 0.6) × 10 3 /T + (18.8 ± 0.5), ln P(Lu 2 Cl 6 ) = (-42.5 ± 0.7) × 10 3 /T + (28.7 ± 0.6), ln P(Lu 3 Cl 9 ) = (-48.3 ± 1.2) × 10 3 /T + (27.0 ± 1.2), ln P(Lu 4 Cl 12 ) = (-46.8 ± 1.2) × 10 3 /T + (22.9 ± 1.2). Ion molecule equilibria have been studied in the temperature range 1000-1100 K and the temperature dependencies of equilibrium constants have been obtained. Enthalpies of sublimation to monomer and polymer molecules, enthalpies of formation of gaseous molecules and ions were evaluated using the second and third laws of thermodynamics. The selected values (298 K, kJ mol -1 ) are as follows: ∆ s H°(LuCl 3 ) = 285 ± 5, ∆ s H°(Lu 4 Cl 12 ) = 415 ± 30, ∆ f H°(LuCl 3 ) = -669 ± 10, ∆ f H°(Lu 4 Cl 12 ) = -3400 ± 35, ∆ f H°(LuCl 4 -) = -1194 ± 10, ∆ f H°(Lu 4 Cl 13 -) = -3972 ± 18, ∆ s H°(Lu 2 Cl 6 ) = 370 ± 10, ∆ s H°(Lu 5 Cl 15 ) = 428 ± 50, ∆ f H°(Lu 2 Cl 6 ) = -1538 ± 15, ∆ f H°(Lu 5 Cl 15 ) = -4342 ± 50, ∆ f H°(Lu 2 Cl 7 -) = -2067 ± 15, ∆ f H°(Lu 5 Cl 16 -) = -4826 ± 30, ∆ s H°(Lu 3 Cl 9 ) = 423 ± 30, ∆ s H°(Lu 6 Cl 18 ) = 392 ± 50, ∆ f H°(Lu 3 Cl 9 ) = -2439 ± 35, ∆ f H°(Lu 6 Cl 18 ) = -5332 ± 50, ∆ f H°(Lu 3 Cl 10 -) = -2982 ± 20, ∆ f H°(Lu 6 Cl 19 -) = -5890 ± 25, The electron affinity of LuCl 4 superchloride molecule has been estimated to be 3.7 ± 1 eV.