The mechanism underlying CD4~+CD25~+Foxp3~+ regulatory T cells(Tregs) promoting the development of colorectal cancer(CRC) was elucidated in the present study. Forty-eight cases of colorectal carcinomas, 22 cases of colon polyps and 21 cases of normal colorectal tissues were collected. The correlation among Foxp3, IL-10 and Stat3, and the clinical relevance of these three indexes were analyzed. The results showed that the levels of Foxp3 expressed in infiltrating CD4~+CD25~+Foxp3~+Tregs, and IL-10 and Stat3 in CRC tissues were all significantly higher than those in polypus tissues and normal colon tissues(P<0.01). Pearson correlation analysis indicated that the expression level of Foxp3 was positively correlated with Stat3 at m RNA level(r=0.526, P=0.036), and was positively correlated with IL-10 at protein level(r=0.314, P=0.030). The Foxp3 expressed in CD4~+CD25~+Foxp3~+Tregs was correlated with the histological grade, lymph node metastasis and TNM stage of CRC(P<0.05 for all). The IL-10 expression was correlated with the histological grade and TNM stage(both P<0.05). The Stat3 expression was correlated with the lymph node metastasis and TNM stage(both P<0.05). It was concluded that CD4~+CD25~+Foxp3~+Tregs can inhibit tumor immunity in combination with some other related inhibitory cytokines and that Foxp3 expression in CD4~+CD25~+Foxp3~+Tregs correlates with CRC progression. The mechanism underlying the development of colorectal cancer (CRC) was elucidated in the present study. Forty-eight cases of colorectal carcinomas, 22 cases of colon polyps and 21 cases The correlation among Foxp3, IL-10 and Stat3, and the clinical relevance of these three indexes were analyzed. The results showed that the levels of Foxp3 expressed in infiltrating CD4 ~ + CD25 ~ + Foxp3 ~ + Tregs , and IL-10 and Stat3 in CRC tissues were all significantly higher than those in polypus tissues and normal colon tissues (P <0.01). Pearson correlation analysis indicated that the expression level of Foxp3 was positively correlated with Stat3 at m RNA level (r = 0.526, P = 0.036), and was positively correlated with IL-10 at protein level (r = 0.314, P = 0.030). The Foxp3 expressed in CD4 ~ + CD25 ~ + Foxp3 ~ + Tregs was correlated with the histological grade, lymph node metastasis and TNM stage of CRC (P <0.05 for all). The IL -10 expression was correlated with the histological grade and TNM stage (both P <0.05). The Stat3 expression was correlated with the lymph node metastasis and TNM stage (both P <0.05). It was caused that CD4 ~ + CD25 ~ + Foxp3 ~ + Tregs can inhibit tumor immunity in combination with some other related inhibitory cytokines and that Foxp3 expression in CD4 ~ + CD25 ~ + Foxp3 ~ + Tregs correlates with CRC progression.