To explore the role of Treg cells in the pathogenesis of idiopathic thrombocytopenic purpura (ITP). The ITP mouse model was established, the Treg cell ratio in peripheral blood and spleen was detected by flow cytometry, the CD4+ CD25+ T cells were sorted by immunomagnetic beads, the Treg cell associated transcription factors (Foxp3, Smad7, STAT5 and Akt-1) and cytokines (IL-10, TGF-β) in CD4+ CD25+ T cells were enriched from spleen mononuclear cells, and the mRNA expression of Treg cell was measured by real-time PCR. The ratio of Tregs in peripheral blood and spleen decreased significantly in ITP mouse, as compared with the controls (P<0.01). In addition, the mRNA expression of IL-10, TGF-β and Foxp3 decreased significantly in spleen CD4+ CD25+ T cells (P<0.05). Expression of Smad 7 mRNA was higher than that of controls. The alteration in Treg frequency and function may be responsible for the immune dysfunction in ITP disease. It is also speculated that the lower mRNA expression of Foxp3 and higher mRNA expression of Smad 7 may inhibit the proliferation and differentiation of Treg cells.