Potassium cobalt hexacyanoferrate (KCoFC) was synthesized for removal of Cs ions in acid waste solution. The synthesized KCoFC. was stable in nitric acid solution of pH= 1 and showed high selectivity for Cs ion over Sr and Na ions. The Kd,cs for 0.01 N Cs ion solution at pH=2 was about 3.6x 103 mL/g in the presence of the same concentrations of Sr and Na ions, respectively. In the binary ion exchange system, both the Dubinin-Polanyi model and Langmuir model fit the experimental data, although the Dubinin-Polanyi model fit more correctly than the Langmuir model. However, in the multi-component system, only the modified Dubinin-Polanyi model, which is a semiempirical equation, fit the experimental data accurately. The ion exchange capacity of KCoFC. for Cs ion obtained by the Dubinin-Polanyi equation was 1.72 meq/g.