A series of biouclear copper (II) complexes containing a-diimine ligand has been synthesized and characterized by electron paramagnetic resonance spectroscopy. The copper complexes of the form [Cu(dien)D](ClO4)2 or [Cu2(dien)2L](CIO4)4, where dien is diethylenetriamine, L' is monodentate ligand and L is bridging ligand, were studied. The EPR spectra were recorded in solution and frozen glassy solution. In the frozen solution spectra, the values of G‖ are in the range of 2.10 to 2.20, and the g⊥ are in the range of 2.03 to 2.06. Furthesmore, the values of A‖ are in the range of 170 to 188 gauss, and the A ⊥ are in the range of 17 to 32 gauss. The data indicate that the structure of Cu(II) complexes is axial symmetry in square pyramidal form.