The dependence of ionic activity and electrode potential upon electrolyte concentration in ethylenediamine includes the effects of ion-pair formation involving all possible combinations of cations and anions represent in the solution and includes the ion-atmosphere effects of dissociated ions. For calculating activity coefficients, Debye-Huckel limiting law, extended Debye-Huckel,equation, and Marshall Grunwald equation were used in comparison of experimental and calculated plots of the electromotive force of the cell versus the logarithum of concentration. The fit of the experimental points to the theoretical curves was improved in case of the Marshall-Grunwald equation.