CD4+CD25(high)FOXP3+ regulatory T cells (Tregs) play an important role in the maintenance of immunological self-tolerance by suppressing autoimmune responses and anti-tumor immune responses. The current model suggests that epithelial tumor cells recruit Tregs to inhibit anti-tumor immunity in the tumor microenvironment, which thus limits the efficiency of anti-tumor immune responses and immunotherapy. However, recent findings on Tregs in lymphomas have complicated this working model. The biopsy specimens of some lymphomas have significantly higher percentages of Tregs than that in tumor-free lymph nodes and normal peripheral mononuclear cells. Higher Tregs numbers in these lymphomas predict improved survival and prognosis of patients. In this brief review, we summarize the progress in following topics: (1) Tregs; (2) Tregs and T cell co-stimulation; (3) Tregs in lymphomas; and (4) Tregs in other Tumors. Further characterization of Tregs in lymphomas and other tumors will provide insight on the differential regulation of Tregs' function and survival, and define the potentials of Tregs-based immunotherapeutics.