Background In haploidentical hematopoietic stem cell transplantation (HSCT),the duration of graft-versus-host disease (GVHD) prophylaxis after modified donor lymphocyte infusion (DLI) was the only risk factor of DLI-associated grades 3-4 acute GVHD.However,the successful application of modified DLI depended not only on the reduction of severe GVHD,but also on the preservation of graft-versus-leukemia (GVL) effect.Therefore,this study was performed to compare the impact of prophylaxis for 6-8 weeks and prophylaxis for ＜6 weeks on GVL effect after modified DLI in haploidentical HSCT.Methods A total of 103 consecutive patients developing hematological relapse or minimal residual disease (MRD)-positive status after haploidentical HSCT and receiving modified DLI were investigated retrospectively.Fifty-two patients received prophylaxis for 6-8 weeks after modified DLI; the remaining 51 patients received prophylaxis for ＜6 weeks.Results First,compared with prophylaxis for ＜6 weeks,prophylaxis for 6-8 weeks reduced incidence of relapse in total patients (26.6％ vs.69.0％,P ＜0.001).Besides,prophylaxis for 6-8 weeks also reduced incidence of relapse in 54 patients developing hematological relapse post-transplant (P=0.018) and in 49 patients developing MRD-positive status post-transplant (P ＜0.001).Second,prophylaxis for 6-8 weeks reduced incidence of acute GVHD (P ＜0.05),reduced the therapeutic application of immunosuppressive agents (P=0.019),but increased the incidence of chronic GVHD (P＜0.05).Third,prophylaxis for 6-8 weeks improved overall survival and disease-free survival in total patients,as well as in patients developing hematological relapse post-transplant and in patients developing MRD-positive status post-transplant (P ＜0.05).Conclusions In haploidentical HSCT,prophylaxis for 6-8 weeks after modified DLI does not reduce GVL effect,but reduces the incidence of DLI-associated acute GVHD compared with prophylaxis for ＜6 weeks.This strategy will probably improve the safety and efficacy of modified DLI further.