The purpose of the present work is to investigate the association of cerous and sulphate ions in aqueous solution. Electromotive force measurements for the cell [formula here] at various ionic strengths have been used together with a prior knowledge of the dissociation constant of the bisulphate ion, to find the dissociation constant of the ion-pair CeSO₄⁺. By making measurements at varying temperatures derived thermodynamic functions of the ion-pair have been obtained.