Thermal conductivity measurement of carbon nanotubes water-based nanofluids is here reported. We have considered in particular the influence of nanoparticle volume fraction, temperature, carbon nanotube aspect ratio and different kind of surfactant (SDBS, Lignin, Sodium polycarboxylate) on thermal conductivity enhancement of nanofluids. The experiments show that TC enhancement of nanofluids produces at very low volume fraction. It is also mainly governed by both volume fraction and temperature increase. However, TC enhancement of nanofluids is weakly affected by carbon nanotubes aspect ratio and surfactant type used in the study. In addition, various theoretical thermal conductivity models are used to possibly correlate the experimental data and explain the TC enhancement of nanofluids. The selected models do not capture the experimental findings within the range of this parametric study, evidencing the need to develop appropriate model for TC enhancement prediction of CNT nanofluids and measure TC of this kind of nanofluids before performing numerical studies in heat exchangers and cavities.