Increases in DNA content within a cell by endoreduplication is widely observed in the metabolically active tissues of a lot of plants and animals. During egg production, insect females synthesize massive amounts of vitellogenin in their fat bodies, and those of some insects become polyploid to accelerate vitellogenin production. Social insects have developed reproductive division of labor, so it is reasonably expected that termite queens would have higher endopolyploidy level in their fat body than non-reproductives. Here we show, queens of termite Reticulitermes speratus have disproportionately higher amount DNA in their fat body cells and the queen-specific endoreduplication occurs along with reproductive development. By DNA content analysis using flow cytometry, we demonstrated that more cells contained 4C-DNA than 2C-DNA in the fat bodies of mature queens. This high level of polyploidization in fat body was not found in non-reproductive castes or immature queens. In this talk, we also demonstrate how the endoreduplication in the fat body is regulated in other termite species. We discuss the evolutionary linkage between endoreduplication in fat body and reproductive division of labor by taking into account the phylogenetic relationship and cost of endoreduplication.