A mass transfer model of silica in a bed of OH- type strong anion exchange resin is proposed, on the basis of the phenomenon that silica is adsorbed into it by both ion exchange and polymerization in the resin. The two self diffusivities of silica in both liquid and resin phases and also the adsorption rate coefficient by the polymerization were determined. Using the presented model and these values, the theoretical breakthrough curves for silica were calculated. The theoretical curves agreed with the experimental data. The effluent behaviour of silica is greatly affected by the pH value and the concentration of the coexisting anion (such as Cl-) of the feed solution.