Background: Graft-versus-host disease (GVHD) continues to compromise the overall success of allogeneic hematopoietic cell transplantation (HCT). Although rates and severity of acute GVHD have decreased with improvements in donor selection criteria, pharmacologic prophylaxes, and supportive care, rates of chronic GVHD have remained remarkably stable at 35% to 50% for many years.   Objective: Aim of this study is the early identification of patients at increased risk of HSCT-related complications, with a focus on acute Graft versus Host Disease, according to IL6 level as a potential biomarker. Serum IL6, measured before conditioning and 7 days after allo-HSCT, to predict main transplant outcomes with PT-Cy. Patients and Methods: In This study we conducted on 40 patients with Hematological diseases from Ain Shams University hospital and Maadi Military hospital, BMT unit, (22 male, 18 female) with age range (18 - 44) years old (Table 1) who underwent Haplo allogeneic stem cell transplant, after obtaining a written informed consent from the patients. In our study 28 patients had Acute GVHD, 18 patients had grade 1 & 2 Acute GVHD 64.3% while, 10 patients had grade 3 & 4 Acute GVHD 35.7%. Results: Skin acute GVHD stage 3-4 patients had high Post-transplant and pre- transplant IL 6 level than patients developed stage 1-2 skin acute GVHD with Mean (345\\\\\\\\\\\\\\\\155) than (105\\\\\\\\\\\\\\\\84) with statistically significant difference P value (0.006, 0.006) respectively. Liver acute GVHD stage I-II patients in our study had high Post-transplant IL 6 level with Mean (243.75) with statistically significant difference P value (0.006). Liver acute GVHD stage I-II patients had Pre-transplant IL 6 level with Mean (113.13) with statistically insignificant difference P value (0.052). GIT acute GVHD stage 3-4 patients had high Post-transplant IL 6 level than patients developed stage 1-2 GIT acute GVHD with Mean (226.67) than (198.89) with statistically significant difference P value (0.003). GIT acute GVHD stage 3-4 in our study patients had low pre-transplant IL 6 level than patients developed stage 1-2 GIT acute GVHD with Mean (86.67) than (108.78) with statistically insignificant difference P value (0.624). IL 6 level was higher pre (117.33 ± 59.67) and post-transplant in post-transplant CMV reactivation cases (209.67 ± 162.34) with p value (0.005, 110 ng/L (P value 0.003).