The role of different circulating lymphocyte subsets, as well as their correlation with clinical characteristics of small cell lung cancer patients have not yet been fully understood. This study aims to evaluate the influence of the fluctuating absolute numbers of lymphocyte subpopulations in peripheral blood of patients with small cell lung cancer. The absolute counts and percentages of lymphocyte subsets in peripheral blood of 329 patients with small cell lung cancer were retrospectively analyzed. The numbers of CD3, CD3CD4, and CD3CD8 T lymphocytes, CD3CD19 B lymphocytes, and CD3CD16CD56 NK cells were evaluated by flow cytometry. Their relationship with the patients' clinical characteristics were statistically evaluated. The CD4/CD8 values derived from the absolute number and percentage of CD3CD4 cells divided by CD3CD8 cells were identical (1.86  ±  0.99). There was no association between any of the lymphocyte subsets levels and age/sex of the 329 patients with small cell lung cancer. The patients with advanced stage had a reduction in CD3 and CD3CD4 T cell counts and a decreased CD4/CD8 ratio. The levels of CD3CD4 T cells, CD3CD19 B cells, CD3CD16CD56 NK cells, and CD4/CD8 ratio were associated with advanced tumor-node-metastasis stage. Patients who had undergone radiotherapy were characterized by lymphopenia with lower numbers of CD3, CD3CD4, CD3CD8 T lymphocyte, B lymphocyte, NK cell, and CD4/CD8 ratio. The evaluation of individual CD4/CD8 ratio should be combined with other clinical parameters. Patients with small cell lung cancer have altered lymphocyte homeostasis. Lymphopenia was a long-lasting feature of the enrolled patients who were treated with radiotherapy. The available lymphocyte subsets levels might be used to manage the clinical treatment scheme.