The effect of storage temperature on the physicochemical characteristics, solubility and gelling properties of soy protein isolate (SPI) with different water activities (a w ) was investigated. SPI with a w of 0.19 (SPI-0.19) was placed in environments with relative humidity (RH) of 33% and 74%. After reaching equilibrium, in 20 days, the samples were named SPI-0.33 and SPI-0.74. For SPI-0.74, modifications in the protein characteristics started during the equilibrium period, with a decrease in the solubility and alterations in both the electrophoretic profile of the soluble proteins and in the gelling characteristics. During the 180-day storage period, SPI-0.19 and SPI-0.33 showed similar behaviours: decrease in protein solubility and alteration in hardness, cohesiveness and microstructure of the gels. These alterations were more pronounced during storage at 45°C than at 25°C, and in SPI-0.33 more than in SPI-0.19. Results suggest that storage conditions – temperature and RH – affect the functional properties of the proteins and the use of the isolates as a functional ingredient.