Water sorption and glass transition of four amorphous sugars (lactose, maltose, sucrose, and trehalose) containing bovine serum albumin (BSA) are investigated. Freeze-dried sugar-BSA samples equilibrated at several water activities ranging from 0 to 0.43 were prepared. Moisture content and glass transition temperature (T-g) were measured. For the all sugars, it is found that BSA lowers T-g at low water activity, and raises it at high water activity. It Is also found that the difference between T-g of the sugar-BSA samples and that of the corresponding amorphous sugar samples (T-go) depends mainly on T-go.