Transient mass transfer process is analyzed for cassava drying (Manihot Esculenta Crantz) in a pack bed. Experiments were performed in a thermally insulated radial dryer, considering cy- lindrical pieces of non peeled cassava with three dif- ferent thicknesses: 4, 6, and 8 mm. The void frac- tions considered were 0.22, 0.49, 0.64 and 0.66, while the temperature values were 50oC and 70oC. The humidity removed from the cassava was measured from 10 pieces randomly selected at the beginning of the process. These pieces were weighed every 15 minutes during a three hours period. From the data gathered a non linear regression model was attained as a function of non dimensional numbers, which is valid for the following ranges: 700≤Re≤1900, 10000≤Sc≤31000, 0<Fo≤4. The fitted regression coef- ficient is 2 adj R = 0.87, and the average error when