The performance of the anion bed in a two-bed deionization process was investigated. Experiments and simulation were carried out with a feed solution concentration of about 0.005N. The prepared solutions were dilute acid of HCl, H2SO4 and a mixture of the two. The bed height was about 40 cm and the flow rate in the range of 75-150 ml/min. Both the binary and ternary models were used to predict the column performance. In both models, it was found that the equilibrium parameters do not affect significantly the breakthrough behavior. This is due to the accompanied neutralization reaction which results in the irreversible form of the rate equation. The experimental and theoretical breakthrough curves show very good agreement especially for the early part of the data. Results of this study suggest that a pseudo-binary or pseudo-ternary model can be used to model the fixed bed deionization process by ion exchange.