Europium isotope effects in the Eu(II)/Eu(III) electron exchange system (EXS) has been studied by means of cation exchange chromatography in the temperature range 308–343 K. The heavier isotope153Eu was enriched at the front part of the europium band, and the values of the observed single stage separation coefficients (ϵ=α-1), of the153Eu/151Euisotopic pair, increased with the increase in temperature as 1.1x10−4, 1.2x10−4, 2.1x10−4and 2.4x10−4, at 308K, 323K, 333K, and 343K, respectively. Based on the experimental data, the logarithm of the isotopic equilibrium constant, InK=ϵo, of Eu(II)/Eu(III) electron exchange system have been calculated. The chromatographic height equivalent to a theoretical plate, HETP, was also calculated and found to decrease with temperature.