The fresh mushroom (Agaricus bisporus) is highly perishable and easy to lose quality during the storage. The packaging system can retard the deterioration of the fresh mushroom. However, the water vapor transmission rates of commodity plastic film are lower than the rate of its transpiration, thus resulting in the moisture condensation in the package, cause of perishable by microbial growth. The possible solution for control a humidity level in the package is using a desiccant. This study was undertaken to develop a novel hygroscopic agent from acidified expanded vermiculite (AEV) and CaCl_2 for fresh mushroom which has greater moisture absorption capacity and maintains powder phased in the packaging system. After acid treatment with HCl, AEV achieved higher porosity and became more hydrophilic. CaCl_2 was mechanically mixed with AEV in different proportions and the hygroscopicity was studied at 4 and 25℃ and different humidity levels of 76, 86 and 96% RH. The best combination AEV60 contained 0.6g of AEV and 0.4 g of CaCl_2 yielding hygroscopicity of 1.735 at 4 ℃ and 96% RH. Pilosof model was selected to mathematically describe the hygroscopic curve and used to calculate the amount of AEV in a certain mushroom package. A 100g of mushrooms were packed in PET tray, then insert 1.5 g of AEV60 in the sachet bag at the bottom of the tray. The samples were wrapped with PP film and storage at 4 and 25℃, respectively. The quality of mushrooms was evaluated throughout the storage period. The result showed that the overall appearance and firmness of mushrooms were greater than control during 10 days of storage. Moreover, treated mushrooms present lower numbers of microbial than without treatment.