Potato starch–water mixtures (10–70% w/w) were treated with high hydrostatic pressure (HHP) at 600, 800, and 1000 MPa at 40 °C for 18 and 66 h, and enthalpy change for gelatinization (ΔHgel), gelatinization temperature (Tgel), and enthalpy change for re-gelatinization of retrograded starch (ΔHretro) were investigated by differential scanning calorimetry. Furthermore, the results were compared with those of samples HHP-treated for 1 h reported in our previous study. The ΔHgel values of 10–50% (w/w) mixtures decreased with increased treatment pressure and with decreased starch content. The 30–60% (w/w) mixtures retrograded, and the ΔHretro values increased with decreased ΔHgel values and with increased starch content. There was little effect of holding time on the values of ΔHgel and ΔHretro. The Tgel values of the 10–50% (w/w) mixtures increased with decreased ΔHgel values and with prolonged holding time