Nanofluids have been attractive for the last few years with the enormous potential to improve the efficiency of heat transfer fluids. This work focuses on the effect of pH and sodium dodecylbenzenesulfonate (SDBS) surfactant on the thermal conductivity of nanofluids. The thermal conductivity was measured by a Hot Disk Thermal Constants Anlyser. The results showed that the thermal conductivity enhancements of Cu-H2O nanofluids are highly dependent on the weight fraction of nanoparticle, pH values and SDBS surfactant concentration of nano-suspensions. The Cu-H2O nanofluids with an ounce of Cu have noticeably higher thermal conductivity than the base fluid without nanoparticles, For Cu nanoparticles at a weight fraction of 0.001 (0.1 wt%), thermal conductivity was enhanced by up to 10.7%, with an optimal pH value and SDBS concentration for the highest thermal conductivity. Therefore, the combined treatment with both the pH and chemical surfactant is recommended to improve the thermal conductivity for practical applications of nanofluid. (C) 2008 Elsevier B.V. All rights reserved.