Abstract: Objective: To determine if there is any defect of CD4⁺ T lymphocyte in the peripheral blood of patients with oral and maxillofacial malignant tumors. Methods: Use MTT dying and flow cytometry assay to identify the lymphocyte stimulation response to PHA or SEB, and the percent of T subset in the peripheral blood of these patients. Results: The percent of CD4⁺ T cell and the ratio of CD4/CD8 in patient group were both higher than those in health group. The response of lymphocyte in patients' peripheral blood to PHA and SEB was lower than that in health group. Conclusion: The immune response of patients with oral and maxillofacial malignant tumors is lower than that of the healthy. There may be some defects on the vβ chain of TCR on CD4⁺ T cell in peripheral blood of these patients.