The stoichiometries and stability constants of copper(II) ions with 1-amidino-O-methylurea have been determined in aqueous solution at different temperatures 200C, 250C, 300C, 350C and 400C with constant ionic strength of 0.5 M KNO3 by using Job’s continuous variation method spectrophotometrically. In all cases, the Job’s curves displayed a maximum at a mole fraction Xmetal=0.5 indicating the formation of complex with 1:1 metal to ligand ratio. It was observed that metal-ligand stability constant decreases with increasing temperature indicating exothermic nature of the reaction. Plots of thermodynamic stability constants versus 1/T gave linear curves indicating high temperature sensitivity for the -NH group of the ligand. The thermodynamic parameters i.e.,
G0,
H0 and
S0 have also been calculated.