Abstract: Objective :To study the frequency of the CD4⁺CD25^high regulatory T cells (Tr) in thepatients with non-small cell lung cancer(NSCLC) and its potencial clinical significance. Methods :Thepercentage of the CD4⁺CD25^high Tr cells in the peripheral blood from 61 patients with NSCLC and 15healthy controls was detected by flow cytometry. Results :CD4⁺CD25^high Tr cells from patients with NSCLC were significantly increased compared with those from the controls, and they was (4.36±2.07)%and (2.04±1.03)% respectively (P<0.01). Furthermore, it was related to the progression of NSCLC:stagesⅠ+Ⅱ,(2.26±0.60)%, stage Ⅲ, (3.28±1.38)% (P<0.05) and stage Ⅳ, (6.06±4.08)% (P<0.05) . Theprognosis of the patients who had higher proportion of CD4⁺CD25^high Tr cells was worse. Conclusion :There is an increase of the proportion of CD4⁺CD25^high Tr cells in peripheral blood of the patients withNSCLC, which probably may be related to immuno-tolerance with NSCLC,suggesting depletion of theCD4⁺CD25^high regulatory Tr cells may be an effective strategy for NSCLC patients.