We apply the chemical solution method to synthesize Cu2O nanofluids: suspensions of cuprous-oxide (Cu2O) nanoparticles in water, and experimentally study the effect of reactant molar concentration and nanofluid temperature on the thermal conductivity. Substantial conductivity enhancement up to 24% is achievable with the synthesized nanofluids. The nanoparticle shape is variable by adjusting some synthesis parameters. The thermal conductivity shows both sensitivity and nonlinearity to the reactant molar concentration and the nanofluid temperature. (C) 2009 Elsevier Ltd. All rights reserved.