In this study, we studied the relationship between beads forming percentage and sodium alginate purity or viscosity, and found for the first time that strength of microencapsules depended mainly on M/G ratio of sodium alginate.The results indicate that if guloronic acid content in sodium alginate was high, strength of microencapsules is good, and vice versa.This conclusion is helpful to obtain better microencapsules, and to develop capsule engineering.