Abstract: The lower viability of freeze- dried microorganism restricts the development and application of fruits and vegetables biocontrol agents,probiotics and starter cultures in some extent,but adding the appropriate protectants can compensate such deficiency widely.This paper summarized the application of protectants in lyophilization,and classifies the protectants from different angles,such as chemical structure,source,permeability,protective phase,and selects some common protectants,such as skimmed milk powder,trehalose,sodium glutamate,to illustrate their protective mechanism and applications.Besides,the paper introduced symergistic methods of protectants to show that using only one protectant during freeze- drying can not achieve ideal viability and the synergism of different protectants will make the commercialization of biocontrol agents and starter cultures possible.