Nanoparticles of copper and copper oxide were synthesized by wire explosion technique in the environment of different ambient air pressure. Copper wire with a diameter of 125 mu m and 6.1 cm in length has been exploded in air at 1 bar, 500 mbar, 100 mbar and 50 mbar. Current density in the order of 10(6) A cm(-2) has been applied to disintegrate the wire by discharging a 1.85 mu F capacitor at 10 kV. It is found that the particle size distribution for nano-sized particles follows the log-normal distribution and the median diameter is found to decrease from 31.3 nm to 23.6 nm as the pressure is decreased from 1 bar to 50 mbar. (C) 2011 Elsevier B. V. All rights reserved.