How to shorten the immune convalescence required after transplantation in recipients is still an austere medicinal problem. Speed-up recovery means less infection opportunity and high survival. In this study, an immune-deficient mouse model was developed by lethally irradiation to evaluate the immune reconstitution effect of N-Succinyl-Chitosan (NSC), a water soluble low molecular weight chitosan derivative, after umbilical cord blood stem cells transplantation, including hematopoiesis parameters detection, T-cell phenotype analysis and pathological comparison; effects of NSC on proliferation of umbilical cord blood stem cell has also been evaluated in vitro. By comparison and analysis, we found the combination of NSC and hematopoietic growth factors could dramatically shorten the time required for the recovery of hematopoiesis, T-cell phenotype and injured spleen after transplantation, suggesting that NSC may hasten the immune recovery and therefore may shorten the time of exposure to life-threatening opportunistic infections in transplant recipients. Moreover, we demonstrated that NSC was effective on the proliferation and clone of umbilical cord stem cell in vitro, suggesting NSC could speed up the immune reconstitution in umbilical cord blood transplantation by enlarge the number of umbilical cord blood stem cell.