The standard electrochemical potential of the Ce/Ce3+ couple in fused (lithium chloride + potassium chloride) eutectic was measured as a function of temperature in the range 673 K to 773 K by a high-temperature galvanic cell technique using the reversible concentration cell : Ta,Ce parallel to x(CeCl3) + (1-x)(0.59 LiCl + 0.41 KCl)/y(AgCl) + (1-y)(0.59 LiCl + 0.41 KCl)parallel to Ag,Ta. The molar Gibbs free energy of formation of CeCl3 and the activity coefficient of CeCl3 at infinite dilution of CeCl3 in the (lithium chloride + potassium chloride) eutectic melt were calculated from the e.m.f. results and auxiliary information from the literature. The results obtained agree satisfactorily with the reported values.