A mathematical model was adopted to analyze a binary fixed-bed adsorption column packed with an ion-exchange resin. Two pairs of organic compounds, o-cresol-benzoic acid and p-chlorophenol-p-nitrophenol, were employed as the adsorbates, A modified Langmuir isotherm with interaction factors eta(i) was found suitable for representing the adsorption equilibrium. Scale-up of the binary adsorption column with respect to column length was effective based on the proposed mathematical model and corresponding methods for estimating the model parameters. The significance of excess concentration in the breakthrough curve was related to inlet concentration, column length, and the difference in adsorption affinity.