【Abstract】ObjectiveTo find a stable and efficient method for ex vivo concentration of CD4+CD25+ regulatory T cells in rats. MethodsCD4+CD25+ regulatory T cells were separated from the rat splenic cells in two steps by magnetic cell sorting (MACS) system. CD4+ T cells were first negatively sorted by cocktail antibodies and antiIgG magnetic microbeads. And then CD4+CD 25+T cells were positively sorted by antiCD25 PE and antiPE magnetic microbeads. The purity and the cell survival rate of the sorted cells were measured by flow cytometry and trypan blue dyeing respectively, and the immunosuppressive action of CD4+CD25+ T cells on the proliferation of CD4+CD25- T cells was also assessed by in vitro cell proliferation assay. ResultsThe purity of negatively sorted CD4+ T cells were (83.6±2.5)% (79%~87%), and the purity of positively sorted CD4+CD25+ T cells was (90.2±1.8)% (86%~93%) with the survival rate of (92.8±3.4)% (92%~95%). These concentrated cells significantly suppressed the proliferation of CD4+CD25- T cells in mixed lymphocyte culture （CD25+/CD25- versus CD25-, P＜0.01）. ConclusionWe created a twostep procedure of magnetic cell sorting system for CD4+CD25+ regulatory T cells sorting, which insures the cells to be satisfactorily purified and well functioned.