A soluble Jagged-1/Fc chimera protein (Jagged-1/Fc) was directly used to induce the differentiation of lymphonode cells in mice into CD4⁺CD25⁺ regulatory T cells in vitro. A fluorescein-labeled monoclonal antibody staining combined with flow cytometry was applied to detect the effect of different doses of Jagged-1/Fc on the differentiation of the lymphonode cells into CD4⁺CD25⁺ T cells at different time, and to measure intracellular cytokine changes of the T cells induced by Jaggde1/Fc. The level of TGF-β1, IL-4 and IL-10 secreted by the T cells that were induced by Jagged-1/Fc was determined by ELISA. The results showed that over 500.0 μg/L of Jagged-1/Fc led to the obvious enhancement of the proportion of CD4⁺CD25⁺ T cells within the day 4 to 6 of induction, which was abrogated with an anti-Jagged-1/Fc monoclonal antibody. This induction action of Jagged-1/Fc on CD4⁺CD25⁺ T cells was also inhibited by the block of a Notch signal pathway with N-[N-(3,5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT). The level of IL-4 and IL-10 in the supernatant of T cell culture and their intracellular level were elevated by the induction of Jagged-1/Fc，and the level of TGF-β1 in the supernatant was not altered. These findings suggest that a soluble Jagged-1/Fc chimera protein may induce the differentiation of mouse lymphonode cells into CD4⁺CD25⁺ regulatory T cells in vitro.