Objective: To investigate the alterations of peripheral blood T cell subsets and their relations with lymph node metastasis and histological grade in breast cancer patients. Methods: The percentages of T cell subsets in peripheral blood in 86 patients with breast cancer and 20 patients with mammary adenosis were determined by flow cytometry. Results: There was no significant difference in percentages of peripheral blood total T cells and CD4+ T cells between breast cancer patients and mammary adenosis patients (both P>0.05), but the percentage of peripheral blood CD8+ T cells in breast cancer patients was lower than that of mammary adenosis patients (P<0.05). In breast cancer patients, the percentage of CD4+ T cells in cases with lymph node metastasis was higher than that of cases without lymph node metastasis (P<0.05); the percentage of CD8+ T cells was increased with histological grade increase (P<0.05). Conclusion: There are cell-mediated immune disorders in breast cancer patients, and the alteration in proportion of CD4+ T cells and CD8+ T cells in peripheral blood is closely related to lymph node metastasis and tumor histological grade, respectively. Monitoring of the alterations in peripheral blood T cell subsets may be helpful for estimation of the disease status and prognosis.