Abstract: By ultrasonic vibration, the carbon-water nanofluids were made from the carbon nanotubes and a certain proportional dispersant in deionized water. Comparing with thermal conductivity and dynamic viscosity, the effects of the mass fraction were analyzed. The test results indicate that the thermal conductivity of multi-wall and single-wall carbon nanofluids are improved with the increasing of carbon particles concentration, but compared with multi-wall carbon nanofluids, the viscosity of single-wall carbon nanofluids greatly increases. Based on the measured results, the multi-wall carbon would be more applicable to heat transfer enhancement.