Objective: It has been widely accepted that lymphatic helper T cells in the lymph system have plasticity. Treg cells, as one of the helper T cell phenotypes, can be induced in different cytokine environment and reveal the existence of plasticity. In addition, lymphocyte function associated antigen 1 (LFA-1) play an important role in the function and migration of lymphocyte differentiation. This study was aimed to investigate the effect of LFA-1 on Treg cells plasticity and the possibility mechanism in vitro. Methods: The high purity Treg cells in wild mice and LFA–1-/- mice pre in vitro, and then cultured in completely medium containing IL-6, IL-23, TGF–beta. On the eighth day, the co-expressing of Foxp3 and IL-17 was measured by flow cytometer, and the expression of STAT3 and ROR gamma t was detected by PCR. The levels of IL-10 and IL-17 in supernatant were measured by ELSIA. Results: Both of the wild mice Treg cells and LFA–1-/- mice Treg cells showed the plasticity in inflammatory conditions, but LFA–1-/- mice Treg cells revealed a higher percentage of Foxp3/IL-17 co-expressing, and the expression of STAT3 and ROR gamma t in LFA–1-/- mice Treg was also increased than that in the wild mice Treg cells(P<0.001). Furthermore, both of the two types of cells supernatants showed that IL-17 is higher with IL-10 decreasing than that of treatment，and the change is obvious in LFA–1-/- mice Treg cells(P<0.001) . Conclusion: LFA-1 has the effect on the plasticity of Treg by regulating the expression of STAT3 and ROR gamma t.