However, there is very few discussion about the suitable size of desiccant unit. Although Nuntaphan et al [5] recommended using the tray-type unit, unfortunately their research did not report the suitable size of tray, in particular the tray thickness. Therefore, in our research, the performance of adsorption and regeneration process of tray type desiccant unit with different tray thickness has been investigated. In addition, the performance of longan dryer with desiccant tray is calculated by using the simulation program.