Abstract: Objectve To compare the effects of T-cell suppression mediated by mesenchymal stem cells (MSC) from normal individuals and chronic aplastic anemia (CAA) patients. Methods MSC were cultured from the bone marrow of 5 healthy volunteers and 10 CAA patients, Morphology, surface markers and the expression of serveral cytokines of MSC were compared, and the effects of T-cell supression were tested in the following assay: phytohemaglutinin (PHA)-primed cultures, mixed lymophocyte reaction (MLR) and cell cycle of T-cell after PHA-primed cultures. Results MSC from normal volunteers and CAA patients were similar in morphology, proliferation and surface markers. The suppression of T-cell proliferation induced by PHA and alloantigens mediated by CAA MSC was significantly lower than that of normal MSC. More T-cells were arrested in G0/G1 phase by normal MSC, while the effects were deficient by CAA MSC. The cytokines TGF-β2, HGF expression were similar in normal MSC and CAA MSC, but TGF-β1, 3, expressed by CAA MSC were reduced comparing with normal MSC. Conclusion Although the morphology, proliferation and cell surface markers of CAA MSC were normal, the T-cell suppression mediated by CAA MSC is deficient, persists indifinitely after immunosuppressive therapy, whether these abnormalitied are relevant to the pathogenesis of aplastic anemia remains to be determined.