We have attempted phase identification of carbon nanosized powders prepared by pulsed wire discharge (PWD) to clarify the cooling process of PWD plasma. To prepare the carbon nanosized powders, carbon fibers were discharged in nitrogen gas at 26 – 101 kPa by PWD. Volume fractions of phases in the carbon nanosized powders were analyzed by thermogravimetric analysis and powder X-ray diffraction. The volume fraction of amorphous carbon, which must be formed by quenching of carbon plasma, was increased with increasing nitrogen gas pressure. This result suggested that the cooling rate of PWD plasma increased with increasing ambient gas pressure.