Nanofluids are advanced concept fluid that solid particles of nanometer size are stably dispersed in fluid likes water, ethylene glycol and others. They have higher thermal conductivities than base fluids. If using this characteristic, efficiencies of heat exchangers can be increased. Therefore in this study, we measured thermal conductivity and viscosity of carbon nanofluids. They were made to ultra sonic dispersed oxidized multi-walled carbon nanotubes(OMWCNTs) in distilled water and ethanol, respectively. The mixture ratios of OMWCNTs were from 0.0005 vol% ~ 0.1 vol%. Thermal conductivity and viscosity was measured by transient hot-wire method and rotational viscometer. The results of an experiment are as in the following: thermal conductivity of the 0.1 vol% pure-water nanofluid improved 7.98% ($10^{circ}C$), 8.34% ($25^{circ}C$), and 9.14% ($70^{circ}C$), and its viscosity increased by 37.08% ($10^{circ}C$), 33.96% ($25^{circ}C$) and 21.64% ($70^{circ}C$) than the base fluids. Thermal conductivity of the 0.1 vol% ethanol nanofluids improved 33.72% ($10^{circ}C$), 33.14% ($25^{circ}C$), and 32.25% ($70^{circ}C$), and its viscosity increased by 35.12% ($10^{circ}C$), 32.01% ($25^{circ}C$) and 19.12% ($70^{circ}C$) than the base fluids.