In the present work, the heat capacities at T = 298.15 K of 1,3-dialkylimidazolium bis(trifluoromethylsulfonyl)imide, [C N/2 C N/2 im][NTf 2 ], were measured, for the first time, using a high-precision heat capacity drop calorimeter, with an uncertainty of less than 0.15%.