A method for estimating the requisite number of equilibrium stages for ion exchange fixed bed is proposed, and a description is given on application of the method to systems of Na+-H+ and Ca++-H+ exchange using Amberlite IR-120. It is found that the number of equilibrium stages depends on the ion exchange system, on the concentration of the liquid phase and on the liquid flow rate. The method proposed is proved valid through comparisons between the values of H.E.T.P. based on the number of equilibrium stages thus obtained and those of H.T.U. obtained independently of N.