Many Gram-negative bacteria use the type III secretion system (TTSS) to inject toxin proteins into host cells, then cause the plague disease, typhoid fever, diarrhea disease etc. Chaperone proteins is one of four components of MTSS and play an important role in helping the secretion of toxin proteins. Although these proteins had been found for almost ten years, the detailed function of chaperones is enigmatic. In this review, a brief introduction is given about the progress of classification, function of chaperones and characteristics of the interactions between chaperones and substrates.