Conclusion: The deficient regulatory T cells may play a role in the development of allergic rhinitis. Objective: A subpopulation of regulatory T cell that produce IL-17a were proved to show an apparent duality of regulatory T cell and effector T helper-17 cells. We studied this subpopulation in patients with allergic rhinitis. Methods: Fresh whole blood from 20 patients with allergic rhinitis and 19 healthy donors was used to investigate the frequencies of CD4(+)IFN-gamma(+) T cells (effector T helper-1), CD4(+)IL-4(+) T cells (effector T helper-2) and CD4(+)IL-17a(+) T cells (effector T helper-17) by flow cytometry after stimulation for 4-6 h. Simultaneously, CD4(+) T lymphocytes were isolated from peripheral blood mononuclear cells and then the frequencies of regulatory T cells and IL-17a-producing regulatory T cells in the allergic rhinitis group were compared with healthy controls after T-cell antigen receptor stimulation for 48 h. The suppressive capacity of CD4(+)CD25(high)CD127(low) regulatory T cells that were stimulated by Dermatophagoides pteronyssinus in both groups was isolated and assessed. Results: The frequencies of effector T helper-17 and effector T helper-2 cells were higher in the allergic group compared with healthy controls. Regulatory T cells were similar in both groups, but IL-17a-producing regulatory T cells were increased in the allergic group. In addition, the capacity of regulatory T cells to suppress effector T helper-17 cytokine production was significantly decreased in the allergic group.