A new amino acid ionic liquid (AAIL) [C(3)mim][Val] (1-propyl-3-methylimidazolium valine) was prepared by the neutralization method. Using the solution-reaction isoperibol calorimeter, molar solution enthalpies of the ionic liquid [C(3)mim][Val] with known amounts of water and with different concentrations in molality were measured at T = 298.15 K. In terms of standard addition method (SAM) and Archer's method, the standard molar enthalpy of solution for [C(3)mim][Val] without water, Delta sH(m)degrees = (-55.7 +/- 0.4) kJ.mol(-1), was obtained. The hydration enthalpy of the cation [C(3)mim](+), Delta H+ ([C(3)mim](+)) = -226 kJ.mol(-1), was estimated in terms of Glasser's theory. Using the RD496-III heat conduction microcalorimeter, the molar enthalpies of dilution, Delta H-D(m)(m(i) -> m(f)), of aqueous [C(3)mim][Val] with various values of molality were measured. The values of Delta H-D(m)(m(i) -> m(f)) were fitted to Pitzer's ion-interaction model and the values of apparent relative molar enthalpy, L-phi, calculated using Pitzer's ion-interaction model. (C) 2011 Elsevier Ltd. All rights reserved.