In this paper, crystal copper nanoparticle clusters, prepared by reduction of CuSO4 in the presence of dendrimers with a trimesyl core (G3-G6), are characterized by Fourier transformation IR (FT-IR), UV spectra and transmission electron microscopy (TEM). The results show that the particle size of the Cu nanoparticles is considerably affected by the generation of the dendrimers as well as the dendrimers concentration. When the concentration ratios of Cu2+ to the G3-G6 dendrimers are 8:1, the average diameters of the particles obtained were 5.6, 4.8. 3.9 and 3.4 nm, respectively. When the concentration ratios of Cu2+ to dendrimers; are 2:1, 4:1, 8:1 and 16:1, the average diameters of the particles are 4.6, 5.1, 5.6 and 6.9 nm for G3, 3.9, 4.3, 4.8 and 5.6 nm for G4, 3.0, 3.4, 3.9 and 4.2 nm for G5 and 2.6, 3.1, 3.4 and 3.8 nm for G6, respectively. The data from the High-resolution transmission electron microscopy (HR-TEM) and electron diffraction indicates that the particles belonged to simple cube crystal structure. (C) 2008 Published by Elsevier B.V.