Background: Anti-PD-1 antibodies (nivolumab) are effective in the treatment of many cancers. There is a demand for less invasive biomarkers. Peripheral and tumor CD8+PD-1+ T cells share neoantigen-specific T-cell receptors (TCRs), and are presumed to act as effector T cells with an antitumor effect at the tumor site. We analyzed the diversity in terms of TCR α and β repertoires on peripheral CD8+PD-1+ T cells, tumor mutation burden and examined the relationship between this diversity and therapeutic effect of nivolumab. Methods: This study used patients administered nivolumab after exhibiting no response to chemotherapy for recurrence following surgery. Peripheral blood mononuclear cells were collected from patients before administration of nivolumab. CD8+PD-1+ T cells were subjected to FACS sorting, NGS-based TCR repertoire analysis was performed by Repertoire Genesis Inc., and TCR diversity was evaluated statistically. This study was approved by the Ethical Committee of Hyogo College of Medicine. Results: Six of 12 patients responded to treatment. Upon comparing these responders (CR, PR) with non-responders (SD, PD), there were no differences in the proportion of PD-1+ in CD8+ T cells and the proportion of CD8+PD-1+ T cells in gated lymphocytes. TCR α diversity was significantly higher among responders than non-responders based on Shannon index, Simpson index and DE50 (P < 0.05, P < 0.05, P < 0.01, respectively). TCR β diversity was also significantly higher among responders than non-responders based on Shannon index, Simpson index and DE50 (all P < 0.01). Progression-free survival (PFS) was 371 days for responders and 148 days for non-responders. Overall survival (OS) was 633 days for responders and 308 days for non-responders, showing a significant difference between the groups. TCR repertoire was proportional to TMB. Clones found in multiple patients were more frequent in indel than in SNP. Conclusions: TCR repertoire analysis was performed on CD8+PD-1+ T cells in easily-obtainable peripheral blood before nivolumab treatment in patients with NSCLC, and nivolumab was observed to be effective in patients with high TCR diversity. This result indicates the TCR diversity of peripheral CD8+PD-1+ T cells is effective as a predictive biomarker for response to ICI therapy.