The mutualism between insects and bacteria, which is an ideal model to study the co-evolution between species, is arousing strong interest from biologists in the recent decade. Blochmannia is the primary endosymbiont in Camponotus ants of Formicidae, and represents the earliest described endosymbiosis between animals and bacteria. Blochmannia is essential for supplementing the nutrients lacking in the host diet, and also plays a key role in maintaining the development and growth, reproduction and nutrition metabolism for the host ants. In our paper, the research progress of the localization, maternal transmission, genomics and functions of Blochmannia are reviewed, which hopefully will provide references for the related research.