Abstract: Objective: To explore the number change of the peripheral blood T lymphocyte subsets(including CD3⁺,CD3⁺CD4⁺ and CD3⁺CD8⁺) and its clinical significance in advanced malignant tumor patients before and after chemotherapy.Methods: The standard chemotherapy in 50 advanced malignant tumor patients were implemented according to the disease kind and clinical stage.The peripheral blood was collected before chemotherapy and after 2 cycles of chemotherapy.The number and ratio of T lymph node cell subsets were detected using flow cytometry,the relationship between the level change of T lymph node cell subsets was analyzed.Results: The number of CD3⁺and CD3⁺CD4⁺ T lymphocyte after 2 cycles of chemotherapy were significantly lower than that before chemotherapy in advanced malignant tumor patients(P<0.01).The number of CD3⁺CD8⁺ T lymphocyte after 2 cycles of chemotherapy were higher than that before chemotherapy(P<0.01).The ratio of CD3⁺CD4⁺ to CD3⁺CD8⁺ cells after 2 cycles of chemotherapy decreased significantly(P<0.01).Conclusions: Monitoring the number of peripheral blood T lymphocyte subsets in advanced malignant tumor patients can assess the immune function,guide treatment and predict prognosis.