Abstract: Objective: To isolate and culture of umbilical cord blood mesenchymal stem cells(UCB MSCs) from human umbilical cord blood and explore the effect of induction indoleamine2,3-dioxygenase(IDO) expresson on the treatment of immune mediated aplastic anemia(AA) in mice. Methods: UCB was collected from full-term deliveries. UCB MSCs were isolated and cultured using the lymphocyte isolation method. The cell morphologhy was observed under inverted microscope,and the surface markers of MSCs were analyzed by flow cytometry. Osteogenic and adipogenic induction was used to verify the differentiation potential of UCB MSCs. The murine model with immune mediated aplastic anemia were established. The caudal vein of mice was injected with UCB MSCs induced by IFN-, and the treatment effect was observed. Results: A little of adherent spindle cells presented at 1 week culture of UCB MSCs. About 3 weeks of culture, these uniformity fibroblast-like cells were found, and showed parallelly or whirlpool-shape arrangement. After passage,MSCs reached 80% confluence at 1 week. Immunophenotype analysis showed that MSCs expressed CD44(94. 36%) and CD73 (92. 48%) ,but no CD34 of hematopoietic marker. UCB MSCs that induced by IFN- promoted IDO activity, and had therapeutic effect on haematogenesis function recovery of mice with aplastic anemia. Conclusions: Under IFN- induction, the isolated and cultured UCB MSCs from umbilical cord blood can improve the IDO activity,which has therapeutic effect on murine immune mediated aplastic anemia.