We identified CD8+ CD122+ regulatory T cells (CD8+ CD122+ Treg cells) and reported their importance in maintaining immune homeostasis. The absence of CD8+ CD122+ Treg cells has been shown to lead to severe systemic autoimmunity in several mouse models, including inflammatory bowel diseases and experimental autoimmune encephalomyelitis. The T-cell receptors (TCRs) expressed on CD8+ CD122+ Treg cells recognize the target cells to be regulated. To aid in the identification of the target antigen(s) recognized by TCRs of CD8+ CD122+ Treg cells, we compared the TCR diversity of CD8+ CD122+ T cells with that of conventional, naive T cells in mice. We analysed the use of TCR-Vβ in the interleukin 10-producing population of CD8+ CD122+ T cells marked by high levels of CD49d expression, and found the significantly increased use of Vβ13 in these cells. Immunoscope analysis of the complementarity-determining region 3 (CDR3) of the TCR β-chain revealed remarkable skewing in a pair of Vβ regions, suggesting the existence of clonally expanded cells in CD8+ CD122+ T cells. Clonal expansion in Vβ13+ cells was confirmed by determining the DNA sequences of the CDR3s. The characteristic TCR found in this study is an important building block for further studies to identify the target antigen recognized by CD8+ CD122+ Treg cells.