The importance of Creatinine in clinical chemistry is well recognized: its level in serum and urine is indicative of renal function (Creatinine Clearance Test) and it is the final metabolic product of Creatine, that participates in energy flow in the muscle tissues. It has been suggested that the metabolism of Creatinine is connected with the complexation to metal ions. However, no thermoanalytical studies on Creatinine complexes are reported in the literature. In this work, the synthesis and the thermal behavior of new Cu-(II)-Creatinine complexes are described. By the coupled TG-FT-IR technique, the proposed decomposition mechanism of the complexes is confirmed. A parallel characterization by solid state IR spectroscopy and mass spectrometry is also reported.