This study was carried out the effects of water activity on the nonenzymatic browning reactions of dry milk powder. Samples (Dry Whole Milk DWM, Nonfat Dry Milk NFDM) stored at 55℃ were analyzed for O₂, CO₂ and H₂O by Gas chromatographic method. The brown color which developed form the Maillard reaction was also measured by a reflective spectrophotometer. And Linear regression equations and the correlation coefficients were determined for O₂, CO₂ and brown color vs. storage, and the results are as follows. The amount of brown and off-flavor development increase as the water activities increase about 0.44 Aw during storage. Both DWM and DFDM milk products show a plateau in water absorption between the 0.33 and 0.44 water activities. DWM produced more browning than NFDM which may be partially due to the carbonyl amine reaction. The CaCl₂ solution may exude a water activity lower than 0.44 and varies greatly with temperatures. Oxygen is depleted as brown color development.