Many studies on the analysis of cations in blood have been reported. However, no suitable method for the pretreatment of blood for the determination of cations by Ion Chromotography. As a result, pretreatment method that the membrane filtration of plasma a diluted 1 to 100 fold acidified pH 3.5 was found to be the most suitable. The recoveris of monovalent cations in blood were yield 101%(Na$^{+}$). 102%(NH$^{+}_{4}$) and 101%(K$^{+}$) Determinations of divalent cations(Mg and Ca ions) in blood by Ion chromatography were summarized as followed conditions Separator Column : CS$_{3}$. Suppressor Column : CMMS. Eluent conen : 25m M-HCl/2mM-Histidine. Regenerant conen: 40mM-Ba(OH)$_{2}$.