Increases in DNA content within a cell due to endoreduplication are widely observed in the metabolically active tissues of plants and animals. During egg production, insect females synthesise 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 labour, wherein queens lay most of the eggs while other individuals have reduced fertility and undertake tasks required for maintaining the colony. Therefore, only queens are engaged in vitellogenin synthesis for egg production in social insects. Here, we show that termite queens have disproportionately more DNA in their fat body cells. Our DNA content analysis using flow cytometry demonstrated that more cells contained 4C-DNA than 2C-DNA in the fat bodies of Reticulitermes speratus queens. This high level of endoreduplication was not found in the fat body cells of other castes. In addition, there was no significant deference in the head cells among caste. This caste- and tissue- dependent doubling of DNA content in fat body cells suggests that termites exploit endoreduplication to boost egg production, in conjunction with the development of reproductive division of labour.