The effect of osmotic dehydration pretreatment (25% NaCl, 80 degrees C, 180 min) on the mass transfer and morphometric characteristics of white mushroom pilei during convective drying (50, 65 and 80 degrees C, 2.0 m/s) is investigated. Samples were characterized during process in terms of their cross-sectional area, inner-to-outer radius ratio and roundness by using image analysis. Drying data were modeled by an unsteady state 2D-diffusion model where product was considered as a hemispherical shell. A novel shrinkage algorithm was applied to move inner and outer radial boundaries at a different rate to reduce geometry mismatch during simulation and reproduce both the change in size and proportions of product. Results indicated that OD pretreatment affected mass transfer characteristics of product by significantly lowering (p < 0.05) estimated water diffusivities in comparison to those observed in fresh samples (1.1-2.9 x 10(-10)m(2)/s vs. 2.6-7.2 x 10(-10) m(2)/s).