The electrochemical behaviour and thermal decomposition of a ternary complex of Cu(II) with saccharin and nicotinamide have been investigated by means of voltammetric (square-wave and cyclic voltammetry), spectroscopic and thermoanalysis (TG, DTA, DTG) measurements. The electrochemical data show that the ternary complex undergoes reduction at a more negative potential (-0.310 V) when compared to the binary complexes; Cu(II)-nicotinamide (a shoulder at -0.164 V) and Cu(II)-saccharinate (-0.252 V). ESR spectra (room temperature) of the complex showed a broad signal (g⊥=2.064) due to the weak anti-ferromagnetic coupling between the Cu atoms. ESR and magnetic susceptibility data suggest that the structure of the complex is square-pyramidal in the solid state. The thermal behaviour of the complex from ambient temperature up to 1000°C in a static air atmosphere was studied. The decomposition pathway of the complex is interpreted in terms of the structural data. A possible mechanism for the decomposition of the complex is proposed. © 2002 Published by Elsevier Science B.V.