Objective To present gene and protein expressions of forkhead/winged helix transcription factor (Foxp3) in the liver of BXSB mice and to explore potential roles of regulatory T cell(Treg) in pathogenesis of hepatic lesions in BXSB mice. Methods We examined the liver expression of Foxp3 in 8-and 16-week BXSB male mice using immunohistochemical staining and real-time PCR, and compared with 8-week normal C57BL/6 male mice as a control. Results In immunohistochemistry，Foxp3 staining in normal control mice was pretty strong as dark brown and distributed in hepatic sinusoid and perisinusoidal space, but in 8-and 16-week BXSB mice the staining was weaker as light brown than normal mice and distributed near limiting plate mainly. The mRNA of Foxp3 was significantly down-regulated in 8-and 16-week BXSB mice liver compared to normal controls(0.30±0.04，0.18±0.03 vs 1.08±0.08,EM>P/EM><0.01), and the Foxp3 expression of 16-week BXSB mice was furthermore downregulated than that of 8-week BXSB mice(EM>P/EM><0.01);Conclusions Distribution and down-regulation of Foxp3 in Treg may play a role in t