The aim of this study is to investigate enhancement of thermal properties of various high temperature nanofluids using Carbon Nanotubes (CNT) for solar thermal energy storage applications. The specific heat of liquid carbonate salt eutectics that are doped with CNT was measured using Differential Scanning Calorimeter (DSC). A eutectic mixture of lithium carbonate (Li2CO3) and potassium carbonate (K2CO3) at a molar ratio of 62:38 is used as the base fluid (solvent). A surfactant (Sodium Dodecyl Sulfate or SDS) was used to obtain well-dispersed suspension of CNT in distilled water. This CNT suspension was added to an aqueous solution of two alkali carbonate salts in the form of a eutectic mixture. The resulting solution was evaporated on a hot-plate to obtain a dry mixture of CNT (at 1% concentration by weight) in the carbonate eutectic. The samples were synthesized for by evaporating at four different hotplate temperatures of 100 C, 120 C, 140 C, and 160 C. The results showed that specific heat capacities of carbonate eutectic-CNT nanofluids were linearly increased as the hotplate temperature was increased. At higher temperatures the water was evaporated faster leading to less agglomeration of the nanoparticles in the nanofluids and thus resulting in higher values of the measured specific heat of the nanofluids.