Modeling of separation of two-component dye mixture has been carried out in an unstirred bath cell. Nanofiltration of a two-component industrial dye-house effluent containing reactive black dye (Cibacron Black B, molecular weight 924.5) and reactive red dye (Cibacron Red RB, molecular weight 855.5) has been considered using a 400 molecular weight cut-off (MWCO) membrane. An unsteady state mass transfer model is developed using an integral method to predict the permeate flux and the permeate concentration of each component. The experimental profiles of permeate concentration and permeate flux are optimized with the calculated profiles to estimate the model parameters. The predicted results using these optimized parameters are in good agreement with the experimental results. (C) 2003 Elsevier Science B.V. All rights reserved.