The complexation reactions between l,3-bis(2-cyanobenzene)-triazene (CBT) with Hg2+ and Cd2+ ions have been studied using spectro-photometry in acetonitrile at various temperatures. The formation constants of die resulting 1:1 and 1:2 (metal ion to ligand) complexes were calculated from the computer fitting of the absorbance mole ratio data. At 25 °C the stability constant of the Hg2+ complex is higher than the Cd2+ complex. The enthalpy and entropy changes of the complexation reactions were also evaluated from the temperature varied formation constants.