The complex microspheres based on sodium alginate（AL） and soy protein isolated（SPI） were prepared by crosslinking the mixing solution with Ca

2+

.With an increase of SPI content

the interactions among components change

resulting in various micro-structure of the complex microspheres.The swelling microspheres after dried show smaller sizes than that of the corresponding original microspheres due to the further formation of hydrogen bonds among components during the evaporation process of water.By treating the microspheres with NaOH aqueous solution

the SPI component dissolves and the some of the Ca

2+

are replaced by Na

+

resulting in the formation of greater inner holes and the shrinkage of the microspheres.