Abstract: An expression is derived for calculating isotope enrichment factor e by displacement chromatography on ion exchanger based on the countercurrent extraction model. The comparation of experimental results with lithium isotopes shows that displacement chromatography could be used successfully for determining the enrichment factor. With highly crosslinking resin, it is shown that ε will decrease with the increase of temperature or the concentration of eluent. The heat of isotope exchange calculated for the highly crosslinking resin-lithium acetate system is-5.03 cal/mole.