Thermal studies by TG/DTA and/or TG/DTG techniques of some mixed-ligand copper(II) chelates were carried out to determine their stabilities and modes of decomposition. The chelates have the formula [Cu(beta -dione)(enR)]X, where beta -dione is the anion of a beta -ketoenol, enR is N,N'-substituted aryl or alkyl ethylenediamine and X is NO3- or ClO4-, while the geometry of the ensuing chromophore CuN2O2 is square-planar. The degradation processes depend on the anions and the substituents of the ligands. The nitrate compounds are decomposed until the stable oxide, CuO, is formed at similar to 560 degreesC in both air and nitrogen. The perchlorate compounds, however, are strong explosives in air and vigorously loose almost all their weight in one step. Ln nitrogen, the thermal profile changes dramatically and instead of explosion a decomposition process takes place affording a metallic residue at similar to 800 degreesC. Mass spectrometry (MS) was also used to give possible fragmentation patterns.