Regarding the drying process of longan, most of farmer prefers to use the bed-type dryer because of its cheaper than other dryers. The Cooperative Promotion Department [2] reported in 2004 that the total number of this bed-type longan dryer is more than 24,000 units in the northern part of Thailand. This longan dryer uses LPG (Liquid Petrol Gas) or diesel oil as a fuel. From the previous study [2], it was found that the thermal efficiency of bed-type longan dryer is about 30%. Many attempts have been made to increase the performance of longan dryer. One method to improve the dryer efficiency is the application of solid desiccant for reducing the moisture of air before entering the combustion chamber of longan dryer. When the moisture of air is decreased, the fuel energy for increasing the air temperature is reduced. Moreover, the adsorption process of desiccant is the exothermic process. Therefore, the outlet temperature of air leaving the desiccant unit is raised and thus this phenomenon promotes the fuel saving too.