Abstract： Objective To evaluate the proportion of CD4+CD25+regulatory T cells(Treg)in peripheral blood of patients with lung cancer and observe the relationship of clinical stage,pathologic types,relation between CD4+CD25+ Treg and lung cancer.Methods Flow cytometer was used to analyze the level of CD4+CD25+ Treg in peripheral blood from seventy-eight cases of lung cancer patients and 30 cases of healthy donors.Results The proportion of CD4+CD25+ Treg in peripheral blood was significantly higher in lung cancer patients(21.07±5.26)%when compared with healthy donors(10.04±2.75)%(P＜0.05).The proportion of CD4+CD25+ Treg was significantly higher in stage Ⅲ or Ⅳ lung cancer patients(22.46±4.35)%,(24.35±6.20)% than in stage Ⅰ and Ⅱ lung cancer patients(12.89±3.19)% and healthy donors(P＜0.05).The proportion of CD4+CD25+ Treg was significantly higher in squamous cell carcinoma(20.75±4.85)%,adenocarcinoma(21.52±5.26)% and small cell lung cancer patients(19.20±6.41)% when compared with healthy donors(P＜0.05)but without significance among each teams(P＞0.05).The proportion of CD4+CD25+ Treg was significantly higher in high differentiation (20.36±3.12)%,middle differentiation(21.11±4.67)% and low differentiation(21.30±5.75)% lung cancer patients than in healthy donors(P＜0.05)but without significance among each teams(P＞0.05).Conclusion The proportion of CD4+CD25+ Treg in the peripheral blood of patients with lung cancer is significantly higher than healthy donors.It plays an importmant role in the progression of lung cancer.The up-regulation of CD4+CD25+Treg is not related with pathologic types.