Solubilities of ammonia in four conventional imidazolium ionic liquids: [C-n mim][BF4] (n = 2, 4, 6, 8) have been measured. Isothermally fixed temperatures are 293.15, 303.15, 313.15, 323.15 and 333.15K; the pressure is from 0 to 1.0 MPa. High solubilities of ammonia are found, and it is also found that the solubilities of ammonia increase when the length of cations' alkyl increases (the ILs have the same anion), that is: [C(8)mim](+) > [C(6)mim](+) > [C(4)mim](+) > [C(2)mim](+). The solubility data have been correlated by the Krichevisky-Kasarnovsky equation, and then Henry's constants and partial molar volumes of NH3 at infinite dilution are obtained. The thermodynamic properties such as solution enthalpy (Delta H-sol), solution Gibbs free energy (Delta(sol)G), solution entropy (Delta S-sol), and solution heat capacity (Delta C-sol(p)) of these systems are obtained. (C) 2010 Published by Elsevier B.V.