To investigate the long term efficacy and side effects of a donor-derived CD19 chimeric antigen receptor (CAR) T-cell (HI19α-4-1BB-ζ CAR-T) therapy in the treatment of patients with relapsed B-cell acute lymphoblastic leukemia (B-ALL) after allogeneic hematopoietic stem cell transplantation (allo-HSCT) . A total of 9 subjects with relapsed B-ALL post allo-HSCT received donor-derived CD19 CAR-T therapy from July 2017 to May 2020. All subjects were infused with donor CD3-positive T cells after lymphodepletion chemotherapy, and a median dose of CAR-T cells was 1.79 (range, 0.86-3.53) ×10(6)/kg. ①All subjects achieved complete remission and MRD-negative at 28-42 d post CAR-T cells infusion. ②Cytokine releasing syndrome (CRS) occurrd in all subjects and was grade 3 in 2, grade 2 in 4, grade 1 in 3 cases respectively. Four subjects developed immune effector cell-associated neurotoxicity syndrome (ICANS) , which was grade 2 in 1, grade 1 in 3. One subject developed grade IV acute graft-versus-host disease (GVHD) , and side effects were all controllable. ③Four subjects relapsed at a median period of 8.6 (4.6-19.3) months, 2 subjects died of disease progression after receiving chemotherapy and another one also died of disease progression 14 months after a second transplant, only 1 subject achieved complete remission after CD22 CAR-T cell therapy. Until last follow-up date, 6 subjects were leukemia-free and achieved complete donor chimerism. The estimated 1-year and 2-year leukemia-free survival (LFS) rate was 63.5% and 50.8%, with a median LFS of 18.1 months. ④After a median follow-up of 25.1 (range, 6.9-36.7) months, the estimated 2-year and 2.5-year OS rate were 87.5% and 52.5%, respectively. The donor-derived CD19 CAR-T cell therapy obtain a high remission rate in relapsed B-ALL patients post allo-HSCT with tolerable side effects, half subjects survived more than 2 years without disease recurrence, though long-term efficacy requires further observation. Chinese Clinical Trial Registry: ChiCTR1900025419.