The results of the application of capillary tube isotachophoresis technique to some EDTA complexes are shown. The stability constant and the kind of counter ion affect to the PR values (Potential grandient of the leading ion/Potential gradient of the sample ion). Different kinds of electrolyte system were used depending on the pH values of the electrolyte. About (19) μl of 0.01 M EDTA complex solution was introduced into the instrument. The migration current was stabilized at 75 μA. The results obtained indicate that the PR values are mainly governed by the valency of the cations. PR values of the EDTA complexes of IIA elements, which have relatively small stability constants, approached to that of the free EDTA when the pH of the leading electrolyte was lowered. This fact might be due to the gradual dissociation of the complexes. When the counter ion in the leading electrolyte had the complexing ability with central metal of EDTA complexes, the PR values of the complexes decreased. The difference in the PR values of each EDTA complexes is increased by this effect, thereby the separation ability of this method is enhanced. Thus, the separation of bivalent and trivalent metal EDTA complexes were easily performed by this method. The linear relation between square root of molecular weights and PR values was obtained for EDTA complexes of IIB elements.