Measurements of the thermal conductivity of ionic liquids are extremely important for current chemical plant design of new environmentally safe processes. Existing data are very scarce and inaccurate. IoNanofluids have emerged as a possible alternative to current engineering fluids for heat transfer applications, namely in small volume heat exchangers. In the present paper we report new data on the thermal conductivity of of 1-n-butyl-3-methylimidazolium bis(trifluoromethanesulfonylimide ([C(4)mim][(CF3SO2)(2)N]) and 1-ethyl-3-methylimidazolium ethylsulfate ([C(2)mim][EtSO4]) at temperatures between (293 and 343) K and IoNanofluids with multiwalled carbon nanotubes based on them, to understand the effect of adding nanomaterials to a ionic liquid matrix and its effect on the mentioned thermal property. The application of existing models to predict the behavior of the IoNanofluids, namely, the enhancement in the thermal conductivity, showed that it is fundamental to understand better the mechanism of heat transfer in these systems, namely, the role played by the interface ionic liquid (cation and anion) nanoparticle, whatever molecular shape they have. A test of the effect of water on the purity of [C(4)mim][(CF3SO2)(2)N] was also performed, and results showed that at any given temperature the thermal conductivity decreases with the amount of water added and that the effect increases with increasing temperature.