Endosymbionts included primary endosymbionts and secondary endosymbionts, accreting with insects. Endosymbionts evolved with insects and benefit from each other. Endosymbiont affected the insects’ growth, insects’ fertilizing and viral disease transmission of plants. GroEL, a 63 kDa protein encoded by the groEL gene of endosymbionts in Bemisia tabaci, played an important role in viral disease transmission by Bemisia tabaci. The product of the groEL gene was a type of viral binding protein. Viral particles that had reached the hemolymph interact with GroEL produced by endosymbionts on their way to the salivary glands and form a complex that protected virions from rapid proteolysis. Begomoviruses were transmitted solely by the whitefly Bemisia tabaci. Several whitefly species, such as Trialeurodes vaporariorum, were able to ingest Bemisia tabaci-transmissible begomoviruses but did not transmit them to plants. In order to probe into the invaded mechanism of Bemisia tabaci, cloning and sequencing of groEL of endosymbionts in Bemisia tabaci long-term living on different host plants in Beijing were conducted. Molecular phylogenetic trees, including groEL genes and GroEL proteins of endosymbionts in Bemisia tabaci and other bacteria,were reconstructed. The results showed that groEL was a very conservative gene and evolved very slowly. There was little difference among groEL genes from endosymbionts in different eco-types Bemisia tabaci. GroEL gene and GroEL protein from endosymbionts in different eco-types Bemisia tabaci belonged to the same branch. Molecular phylogenetic trees based on groEL and GroEL could explain phylogenetic relationships of different bacteria, but not for different eco-type species. There were identical molecular phylogenetic trees for groEL and GroEL. Comparison of GroEL sequences showed that: There were identical conservative amino acids, ATPase activity sites, polypeptide binding sites and GroES binding sites between GroEL of endosymbionts in Bemisia tabaci and other prokaryotic GroEL. GroEL of Bemisia tabaci endosymbionts belonged to typical hsp60. There were a few replacement sites in conservative amino acids of GroEL of endosymbionts in different ecological Bemisia tabaci. These amino acids might be unimportant functional sites. Those results explained that groEL varied in unimportant sites in order to fit into different ecological environment, and kept consistent in necessary functional sites in order to have necessary physiological functions. Further investigation into GroEL would provide insights into valuable ways of controlling plant viral diseases transmitted by Bemisia tabaci. To understand the damage mechanism of pests, it was also very important to investigate the role of the endosymbionts and GroEL.