Synthesis and characteristics of Cu nanopowder were considered by in-situ characterization method using SMPS in pulsed wire evaporation process. With increasing pressure in chamber, particle size and degree of agglomeration increased by increase of collision frequency. Also, it was found from the XRD analyses and BET measurements that crystallite size and particle size decreased with elevating applied voltage. However, SMPS measurements and TEM observation revealed the increase of particle size and degree of agglomeration with increase of applied voltage. These results suggested that particle growth and agglomeration depend on overheating factor in chamber at the early stage and thermal coagulation in filtering system during powder formation until collection.