Ultra-fine Copper particles for a conductive paste in electric-electronic field were prepared using wet-reduction process with hydrazine hydrate ( N 2 H 4 ?H 2 O ) as a reductor. The effect of reaction conditions such as the amount of dispersion ( Na 4 O 7 P 2 ?10H 2 O ) and reductor ( N 2 H 4 ?H 2 O ) on the particle size and shape for the prepared Cu powders was investigated. The quantity of dispersion and reductor varied from 0 to 0.0025 M and from 5 to 40 ml at a reaction temperature of 70 ? C , respectively. The particle size, shape, and structure for the obtained Cu particles were characterized by means of XRD, SEM, TEM, EDS and TGA. The aggregation of Cu particles was reduced with relatively increasing of the amount of dispersion at fixed other reaction conditions. The smaller Cu particle with size of approximately 300nm was obtained from 0.032 M CuSO 4 with adding of 0.0025 M Na 4 O7P 2 ?10H 2 O and 40ml N 2 H 4 ?H 2 O at a reaction temperature of 70 ? C .