Thermal conductivity enhancement of nanofluids can be affected by measurement deviation and particle size distribution. In the present work, deionized water (DW) and ethylene glycol (EG) based nanofluids were made and characterized. A nanofluid thermal conductivity measurement system founded on transient hot wire method was built up and a comprehensive analysis regarding measurement error was made for the two base fluids. The proper hot wire working current and the measurement time were acquired to decrease the measurement error caused by non-constant heating power and natural convection. Then, the nanofluid thermal conductivity was measured with optimized measuring parameters. It was found that the thermal conductivity increases 3.2% and 9.6% for 0.5 vol.% SiO2-EG and 1.0 vol.% SiO2-EG, higher than the result for DW based nanofluids (1.0% and 3.4%). This may be attributed to the higher value of lambda(Brownian) and the difference in particle shape distribution.