Department of Chemistry, Manipur University, Canchipur, Imphal-795 003, India Fax: 91-0385-221429 Manuscript received 29 February 2000, revised 15 January 2001, accepted 16 January 2001 Conductance of diarnmine-bis-1-amidino-o-methylureacobalt(III) monochioride has been measured in water and varying water + methanol (W-M) mixtures at 5-40°. The limiting equivalent conductance (\(\Lambda_o\)) and the ion-association constant (KA) for the complex salt in these mixtures have been evaluated using Shedlovsky equation. Based on the composition dependence of the Walden product, the influence of the mixed solvent composition on the solvation of ions has been discussed. Temperature variation of the association constant has also been studied to evaluate the thermodynamic parameters. The results have been discussed in terms of ion-ion, ion-solvent and solvent-solvent interactions.