Abstract: By two-step method, the carbon-water nanofluids were made from the carbon nanotubes and a certain proportional dispersant in deionized water. The influences of mass fraction, diameter of carbon nanotubes on the solidification and melting properties of nanofluids were studied by differential scanning calorimetry(DSC). The experiment results indicated that the onset temperature of solidification and solidification temperature increased with increasing mass fraction of carbon nanotubes, and compared with the same mass fraction of multi-wall carbon nanofluids, the solidification temperature of single-wall carbon nanofluids increased more. The fusion temperature wasnt affected by mass fraction of carbon nanotubes, the latent heat decreased with increasing mass fraction of carbon nanotubes.