Cu(II) complexes of some heterocyclic ligands such as 2,2'-bipyridyl and 1,10 –phenanthroline, were synthesized. The complexes were characterized by elemental analyses, thermal analyses, IR spectra, electronic spectra, magnetic moment measurement and conductivity measurements. They were found to have the following compositions: 1 2 CuLCl2 , CuL Cl2     , 1 2 2 2 CuL Br  .2H 0 and 2 2 2 2 CuL Br  .3H 0, where L1 = 2,2' -bipyridyl(bipy) and L2 =1,10 - phenanthroline(phen). The complexes which are four coordinated, appear to possess square planar geometry while the six coordinated complexes have distorted octahedral geometry.Thermodynamic parameters such as activation energy (Ea*), enthalpy change (DH ) and entropy change (DS ) for dehydration and decomposition reactions of the complexes, were evaluated using some standard methods. The order of stability of the complexes (with respect to thermal decomposition temperature and Ea* from TGA curve) follows the trend: phen > bipy.