Abstract: Objective　To explore the curative effect and prognosis of umbilical cord blood in the treatment of hematological diseases in children. Method　The clinical data of 51 children who underwent umbilical cord blood transplantation from January 2011 to June 2016 were analyzed retrospectively. Results　In 51 children (34 males and 17 females) with median age of 62 months, 32 children had malignant hematologic diseases and 19 children had nonmalignant hematologic diseases. Two children died before the granulocytes were reconstructed, 4 children had primary implantation failure, and 45 children had successfully implantation. The median time of implantation was 16 d, and the median time of platelet implantation was 23 d. The incidence of peri-implantation syndrome was 46.94%. The 100 day survival rate and long-term overall survival (OS) in children with peri-implantation syndrome were (73.9±9.2)% and (50.2±11.7)% respectively, which were significantly lower than the OS (100%) in children without peri-implantation syndrome (P<0.01). The incidence of acute graft versus host disease (aGVHD) was 55.10%, among which Ⅱ-Ⅲ degrees of aGVHD was 28.57% and Ⅳ degrees of aGVHD was 26.53%. The 100 day OS in children with Ⅳ degrees of aGVHD was （61.5±13.5）%, and The OS in children with Ⅲ and Ⅳ degrees of aGVHD were (75.0±21.7)% and (44.9±14.1)% respectively, and the OS in children without aGVHD was (90.2±6.6)%. The difference was statistically significant (χ2=14.35， P=0.002). The incidence of chronic GVHD (cGVHD) was 28.57%. The long-term OS in children with cGVHD was (72.7±13.4)%, while OS in children without cGVHD was 100%. The 100 days OS was (86.0±4.9)%. Long-term OS in cord blood transplantation was (77.9±6.3)%, among which OS for malignant hematological diseases was (76.6±7.8)% and OS for nonmalignant hematological diseases was (79.5±11.3)%. Among malignant hematological diseases, the OS in acute lymphoblastic leukemia (ALL) was (87.5±11.7)%, OS in acute myeloid lymphocytic leukemia (AML) was (76.7±10.3)%, and OS in myelodysplastic syndrome (MDS) was (33.3±27.2)%. Conclusions　Umbilical cord blood transplantation is an effective treatment for hematologic diseases in children. It is important to treat the peri-implantation syndrome. Prevention and treatment Ⅲ/Ⅳ degree of aGVHD and cGVHD are important strategies to improve the efficacy of umbilical cord blood transplantation.