ObjectiveTo investigate the levels of regulatory T cells (Treg) and FoxP3 gene in patients with gastric cancer before and after operation. MethodsTwenty patients with definite diagnosis of gastric cancer and 15 healthy volunteers were selected. The levels of Treg and T cell subsets in peripheral blood were determined by detecting of CD4 and CD25 with immunefluorescence stain and flow cytometry, the expressions of FoxP3 mRNA in these Treg were detected by RTPCR technique. The expression of FoxP3 protein in the gastric cancer tissue was measured by immunohistochemistry assay. ResultsThe percentage of Treg cells in total CD4+ T isolated from the patients with gastric cancer was higher than that of healthy volunteers 〔(19.39±5.58)% versus (9.91±3.23)%, Plt;0.01〕, and it markedly decreased after operation 〔（13.50±5.93）% versus (19.39±5.58)%, Plt;0.05〕. The FoxP3 mRNA expression in the patients with gastric cancer was also higher than that of healthy volunteers (0.86±0.03 versus 0.64±0.02, Plt;0.01), and decreased after operation (0.73±0.04 versus 0.86±0.03, Plt;0.05). The percentage of CD4+T cell in mononucleocytes of peripheral blood of patients with gastric cancer was significantly lower than that of healthy volunteers (Plt;0.01), but the difference was not significant between before and after operation. FoxP3 protein expressed in cytoplasm of 13 patients with gastric cancer, in which bly positive in 2 cases, middle positive in 6 cases, weakly positive in 5 cases. FoxP3 protein didn’t express in cytoplasm of 7 patients with gastric cancer. ConclusionsTreg may have a significant effect on the onset and development of gastric cancer through immunosuppressive effect. Tumor tissue is an important initiating agent on Treg proliferation.