This article contains water vapor sorption data obtained on amorphous blends of octenyl succinic acid-modified (denoted as hydrophobically modified starch; HMS) and sucrose (S) in the anhydrous weight HMS/S ratios between 100/0 and 27/75. The water vapor sorption data was obtained gravimetrically. The amorphous state of the blends was confirmed by X-ray diffraction. The glass transition temperatures of the phase-separated blends are listed; the blends show phase separation into a sucrose-rich phase and a HMS-rich phase, the composition of which varies with the blend ratios. The sucrose-rich phase is characterized by a glass transition temperature Tg,lower that is 40 to 90 K lower than the glass transition temperature Tg,upper of the HMS-rich phase.