Copper nanosized powders were prepared by pulsed wire discharge (PWD) in NZ gas at low pressure (130 Pa) with high-speed gas puff. The pressure around one of the electrodes was changed to investigate the effect of electrical discharge prevention by gas puff: The peak pressure was changed from 22 kPa to 10 kPa in the gas puff apparatus by changing the distance from an acrylic resin tube and a bottom plate. The energy deposition in the copper wire at 22,15 and 10 kPa was about 40, 37 and 33 J, respectively. The energy deposition in the wire increased with the increase in pressure around the electrode.