The theoretical enthalpies of formation of 108 [AA]X and [AAE]X type amino acid ionic liquids composed of 12 amino acid cations (Gly(+), GlyC(1)(+), Ala(+), AlaC(1)(+), Pro(+), ProC(1)(+), Phe(+), PheC(1)(+), Val(+), ValC(1)(+), Leu(+), LeuC(1)(+)) with 9 different anions (Cl-, BF4-, PF6-, N(CF3SO2)(2)(-), CH3CO(2)(-), CF3CO2-, CF3SO3-, HSO4-, SO42-) were studied. A systematic theoretical study on these amino acid ionic liquids was performed by quantum chemistry calculation using the Gaussian03 program. The geometric optimization and the frequency analyses were carried out using the B3LYP method with the 6-31+G** basis set. Their calculated enthalpies of formation were derived from the single point energies carried out with the MP2/6-311++G** level of theory. The enthalpies of formation of these amino acid ionic liquids were calculated to be from -2577.0 kJ.mol(-1) to -311.3 kJ.mol(-1). The negative values show their stable thermodynamics status. The energy differences between the predicted enthalpies of formation of each amino acid salt and those of their two neutral precursors were studied. The experimental enthalpies of formation of five amino acid ionic liquids [Gly]Cl, [Ala]Cl, [Ala]HSO4, [Pro]CF3CO2, and [Pro]CF3SO3 were obtained from the corresponding energies of combustion determined by the bomb calorimetry method. The experimental enthalpies of formation are in good agreement with corresponding theoretical results. This study provides an effective theoretical method to predict the thermodynamic stability of the preparation of new amino acid ionic liquids.