A new pore-surface diffusion model (PSDM) for batch adsorption systems based on shrinking core theory has been developed. The new PSDM incorporates pore and surface diffusion into a variable effective diffusion coefficient, but the contributions from both pore and surface diffusion are evaluated independently. A further advantage of the new model is that it incorporates a time dependent surface diffusivity based on surface adsorbate concentration. The predicted results have been compared using four sets of experimental data for the batch adsorption of dyes on pith.