A batch-type experimental dryer with an online weighing mechanism was developed for determining the thin-layer drying behaviour of onion. Thin-layer drying rates of brined onion slices were experimentally determined at four levels of drying air temperature (range of 50-80 degrees C), four levels of air flow velocity (range of 0.25-1.00 m/s) and three levels of air relative humidity (range of 10-20%). The experimental data obtained were fitted into an Arrhenius-type model and power model using non-linear regression analysis. The Arrhenius-type model was found to be more suitable for predicting drying rate constants.