The water sorption behavior at 25°C and glass transition temperature (Tg) of mussel meat protein hydrolysate powder without and with maltodextrin 10 DE or gum arabic at 15 and 30% (w/w) were studied in this work. The sorption isotherms were determined by the gravimetric method, and the glass transition temperature was obtained by differential scanning calorimetry (DSC) after powder conditioning at various water activities. Sorption isotherms data were well fitted by a modified Brunauer-Emmett-Teller (BET) model. Powder without additives showed the highest water adsorption followed by those produced with 15 and 30% of carrier agent, respectively. The Gordon-Taylor model was able to predict the effect of water on the glass transition temperature. At 25°C, the critical water content that ensured the glassy state of the mussel hydrolysate powder during storage increased from 0.05 to 0.12 g water/g product and the critical water activity increased from 0.24 to 0.60 when the concentration of carrier agents was increased to 30%.