Abstract Properties and storage stability of spray-dried emulsions stabilized by unheated and preheated (95°C, 15min) soy protein isolates, alone or in combination with lactose, were investigated. In general, the heat pretreatment greatly improved retention efficiency (RE), redispersion behavior, glass transition temperature (Tg) and thermal stability of the emulsion powders, but accelerated instability of the reconstituted emulsions. Additional blending with lactose further considerably improved the RE and dissolution behavior, but significantly decreased the stability of reconstituted emulsions and Tg. Storage at 75% relative humidity resulted in considerably increased droplet size of reconstituted emulsions, as well as decreased RE, wettability and Tg, especially in the powders containing lactose. Microscopic observations confirmed that the changes in properties and stability of the powders upon storage were closely related to rupture of particle structure, and/or particle agglomeration. These findings provide fundamental understanding for the development of microencapsulated products using soy proteins as the wall materials.