The development and function of CD4⁺ CD25⁺ Foxp3⁺ regulatory T cells (Tregs) are strictly regulated by cytokines. Here we show that transforming growth factor‐β (TGF‐β) and interleukin‐4 (IL‐4) play a crucial and antagonistic role in the development of Tregs. Additionally, these cytokines also have distinct effects on the maintenance of natural (nTregs) and antigen‐induced (iTregs) Tregs. Using double‐staining and tracking of proliferation of purified and carboxyflourescein succinimidyl ester (CFSE)‐labelled mouse T‐cell subpopulations we demonstrated that CD4⁺ CD25⁺ Foxp3⁺ iTregs develop upon alloantigenic stimulation in the presence of TGF‐β exclusively from CD4⁺ CD25⁻ Foxp3⁻ precursors. Both the induction of Foxp3 expression and Treg proliferation were prevented when the cells were stimulated in the presence of IL‐4. By contrast, nTregs did not proliferate in the presence of the antigen and TGF‐β, and partially lost their Foxp3 expression. IL‐4 not only prevented the development of iTregs, but also down‐regulated the level of Foxp3 mRNA and decreased the number of Foxp3⁺ cells in a population of iTregs. Further analyses proved that IL‐4 decreased the expression of Foxp3 only in a population of iTregs, whereas it substantially supported the survival of nTregs. Functional experiments showed that Tregs induced in the presence of alloantigen and TGF‐β inhibited, on a per‐cell basis, cell proliferation comparably to nTregs, and their suppressive capacity was not modulated by IL‐4. These data suggest that TGF‐β and IL‐4 differentially regulate the development of Tregs and distinctly sustain Foxp3 expression and the number of nTregs and iTregs, but have no influence on the suppressive activity of Tregs on a per‐cell basis.