Glass transition temperatures of freeze-dried horse mackerel muscle conditioned at various water activities at 25 degrees C were determined by differential scanning calorimetry (DSC). High Moisture content(>0.33 g/g, d.b.) samples obtained by adding liquid water into freeze-dried samples, were also analyzed. The state diagram was composed of the freezing curve and the glass transition line, which were fitted according to Clausius-Clapeyron model and Gordon-Taylor model, respectively. The state diagram yielded maximally freeze-concentrated solutes at 0.786 solids with the characteristic temperature of glass formation being -83.1 degrees C. The state diagram of horse mackerel Muscle developed in this work could be used to predict the stability during frozen storage and in dried conditions as well as in designing drying and freezing processes. (C) 2009 Elsevier B.V. All rights reserved.