Abstract: A method is proposed for the separation of alkali metals by ion exchange chro-matography using dibenzo-18-crown-6 (DBC) -formic acid -hydrochloric acid as eluant, The distribution coefficients (KD) of alkali metals (Na, K, Rb and Cs) between ion exchange resin and solution containing DBC were determined. The effects of DBC on the behavior of ion exchange of the above mentioned elements were studied. A decrease in AD of Na+, K+, Rb+ and Cs+ is found in the presence of DBC in the eluant, and this decrease is remarkable for Na+ and K"1", considerable for Rb+, and very slight for Cs"1"-The KD of these elements were determined as a function of DBC and hydrochloric acid concentration, and were found to be inversely proportional to DBC concentration, coresponding to Delphin's10 equation. The derived equation describing the relation of the KD with hydrogen ion concentration is as follows:in whichwhere KD-the distribution coefficient, C-the exchange capacity of the used resin, Keqo - the stable constant of the complex, Keq1 and Keq2- the equilibrium constants of ion exchange of alkali metals and their DBC complexes respectively. When the DBC concentration is not changed, m is a constant.All the values of KD observed in this experiment agree with the above mentioned equation.The proper condition and results for the separation of the following groups (K-Rb -Cs, Na-Rb-Cs, Li-Na-K-Rb-Cs) are given.