Abstract: Abstract: To improve the storage stability and optimize the storage condition, the effects of different additives on the moisture adsorption isotherms and glass transition temperature of oatmeal were investigated based on the water activity (aw) concept and glass transition theory. Moisture adsorption isotherms of pure oatmeal (PO), oatmeal added with 10% (dry basis, d.b.) maltodextrin (PO-10%MD), 10% (d.b.) whey protein isolate (PO-10%WPI), and a combination of 5% (d.b.) maltodextrin and 5% (d.b.) whey protein isolate (PO-5%MD-5%WPI) were determined at different temperatures (15, 25 and 35oC) using a static gravimetric method. Equilibrium moisture content (EMC) data were fitted with GAB and BET models to select an optimal adsorption isotherms model. Meanwhile, differential scanning calorimetry was used to determine the glass transition temperature (Tg) of PO, PO-10%MD, PO-10%WPI, PO-5%MD-5%WPI and the Tg data were fitted to Gordon-Taylor equation. The effect of maltodextrin (MD) and whey protein isolate (WPI) on the critical water activity (CWA) and critical water content (CWC) of oatmeal was investigated. The results showed that the adsorption curves of oatmeal followed a typical type II (sigmoid) shape, which could be best fitted by GAB model. The EMC of PO, PO-10%MD, PO-10%WPI, and PO-5%MD-5%WPI increased with increasing aw and decreased with increasing temperature. Tg decreased with increasing water content. Addition of MD and WPI significantly increased the Tg of oatmeal. At 25oC, the CWC of PO, PO-10%MD, PO-10%WPI, and PO-5%MD-5%WPI were 0.054 g/g, 0.060 g/g, 0.056 g/g and 0.056 g/g, while the CWA of PO, PO-10%MD, PO-10%WPI, and PO-5%MD-5%WPI were 0.126, 0.175, 0.138, and 0.139, respectively. Therefore, the oatmeal with addition of 10% MD can significantly increase the CWC and CWA, thereby improving the storage stability of oatmeal. The results will provide valuble information for selecting suitable packing materials and establishing optimum storage conditions of oatmeal.