A three-parameter model based on unsteady state mass transfer has been developed for the prediction of flux and rejection during ultrafiltration in unstirred batch cell, Once the three parameters, viz. membrane hydraulic resistance, solute permeability and reflection coefficient, have been ascertained for a particular membrane-sol Lite combination. the flux and rejection could be predicted at any operating condition. The main feature of this model is that it allowed variation of solute diffusivity with concentration in the boundary layer whose effect is more pronounced in the case of unstirred batch cell. Orthogonal collocation on finite element (OCFE) technique has been used to solve the resulting non-linear partial differential equation, coupled with an equation from irreversible thermodynamics. Average deviation between theoretical results and the experimental data generated in this study is found to remain within +/- 5%.