Few studies on the irradiation effects on dehydration characteristics and quality of dried-product have been reported in the past three decades. This study focuses on drying characteristics of bio-products by hot-air after they are pretreated by gamma irradiation. Experiments were made to study the influence of different irradiation dose, air temperature, slice thickness of apple on the dehydration rate, and appearance quality (L-values), vitamin C content, and the rehydration ratio of dried apple. A conclusion is reached that the three factors of irradiation dose, hot-air temperature, and initial slice thickness significantly affected the four indices of appearance quality (L-values), vitamin C content, dehydration rate and rehydration ratio. (C) 2002 Elsevier Science Ltd. All rights reserved.