Emulsions of soy oil in 95 ℃ 15 min heat-treated SPI solutions and/or in addition with lactose solution were prepared and subsequently spray-dried to yield powders, some of them were then stored at 75 % relative humidity to record moisture sorption isotherm within 7 days and get sample when equilibrated. The emulsions were characterized by droplet size distribution before spray drying and after dissolution of dry and wet powders. Also moisture content, microencapsulation efficiency (ME), dissolution rates were determined and micro-structure was established by scanning electron microscopy (SEM). It concluded that heat treating and addition with lactose could greatly increase ME of SPI-stabilized emulsions than that of untreated emulsions, which was up to 98.68%, powders containing lactose performed well encapsulation properties but humid atmosphere highly affect them.