Predicting moisture loss is important when developing a model for vacuum frying, because one of its objectives is to remove food moisture. A diffusion model was considered to describe moisture transfer during vacuum frying. Granny Smith apple slabs were processed at 16.6, 13.3, and 8kPa and between 80 and 120 degrees C. Moisture diffusivity was determined, obtaining a close fit between the model and the experimental data. Diffusivity increased with temperature and decreased when pressure increased. A direct proportionality between heat and mass transfer was observed. Temperature influence was interpreted by the Arrhenius relationship and there was no observed effect of pressure on the activation energy.