Thin-layer drying of amaranth grain was conducted at 40, 50, 60 and 70 degreesC and a moisture range from about 32.5% to 5.0%, dry basis. A mathematical model based on Fick' s second law of diffusion with variable diffusion coefficient for spherically shaped grain was used to predict the drying behavior of the grain. An analytical expression describing the variation of the diffusion coefficient with moisture was derived, based on the fact that the ratio of activation energy for diffusion and the heat of desorption is a constant value and equal to 0.5. A correlation describing the activation energy of the drying process with moisture content and temperature is established. (C) 2004 Published by Elsevier Ltd.