The article reports a simple, economical and highly productive synthesis process of cuprous oxide (Cu2O) and copper/cuprous oxide (Cu/Cu2O) nanoparticles with an average size of below 30 nm. A hydrolysis of copper (Cu) particles (200 nm or even microsize) employing low energy ball milling in aqueous circumstance results a controlled synthesis of Cu2O and cermets of Cu/Cu2O nanoparticles. Ground particles are found both in nanobar and spherical shape with cluster nano-clouds into aqueous solution. X-ray diffraction patterns of the sample powder confirm Cu2O nanoparticles and Cu/Cu2O cermets synthesized by complete and incomplete oxidation of Cu particles, respectively. The process is accomplished at room temperature in presence of de-ionized (DI) water and controlled by changing milling period and ball sizes. Enhanced thermal conductivity of Cu2O-water and Cu/Cu2O-water nanofluids are recorded and compared with non-ground Cu-water nanofluids. (c) 2013 Elsevier B.V. All rights reserved.