Objective To observe the expression of myeloid-derived suppressor cells (MDSCs) in lung tissues of tumor-bearing mice. Methods Twelve C57BL/6 mice were randomly divided into experiment group and control group, with 6 mice in each group. 3LL cells (0.3×106) cultured in vitro were injected into tail vein of mice in experiment group, and mouse lung tissues were obtained three weeks after tumor formation. Lung single cell  suspension was made with mixture of enzyme, and the expression of MDSCs (GR1-FITC and CD11b-PE double positive staining) was detected by flow cytometry. PBS was injected into tail vein of mice in control group, and the following treatment was the same as that in experiment group.ResultsMDSCs were highly expressed (19.92%±6.08%) in lung tissues of mice in experiment group (GR+CD11b+ double positive staining), that in control group was 7.06%±2.67%, and there were significant differences between two groups (P<0.001）. Conclusion MDSCs are highly expressed in lung tissues of mice with lung cancer.