The sequence of complementarity-determining region 3 of the T-cell receptor (TCR) varies widely due to the insertion of random bases during V-(D)-J recombination. In this study, we used single-cell VDJ sequencing using the latest technology, BD Rhapsody, to identify the TCR sequences of autoreactive T-cells characteristic of Japanese type 1 diabetes mellitus (T1DM) and to clarify the pairing of TCR of peripheral blood mononuclear cells from four patients with T1DM at the single-cell level. The expression levels of the TCR alpha variable (TRAV) 17 and TRAV21 in T1DM patients were higher than those in healthy Japanese subjects. Furthermore, the Shannon index of CD8+ T cells and FOXP3+ cells in T1DM patients was lower than that of healthy subjects. The gene expression of PRF1, GZMH, ITGB2, NKG7, CTSW, and CST7 was increased, while the expression of CD4, CD7, CD5, HLA-A, CD27, and IL-32 was decreased in the CD8+ T cells of T1DM patients. The upregulated gene expression was IL4R and TNFRSF4 in FOXP3+ cells of T1DM patients. Overall, these findings demonstrate that TCR diversity and gene expression of CD8+ and FOXP3+ cells are different in patients with T1DM and healthy subjects. Keywords: T-cell receptor; genetic research; genetic screening; single-cell RNA sequencing; type 1 diabetes.