Background: In developing countries, cytomegalovirus (CMV) seropositivity has been widely propagated. Following hematopoeitic stem cell transplantation, the apparent risk of CMV reactivation increases. With effective surveillance and study of the effect of some factors on CMV reactivation, timely treatment with anti-viral treatment may decrease morbidity and mortality associated with CMV reactivation. Aim: This study aimed to evaluate the effect of some factors on CMV reactivation in allogeneic hematopoietic stem cell transplantation (HSCT). Materials & Methods: We retrospectively analyzed 25 patients with Serostatus positive of CMV IgG antibodies who underwent allogeneic hematopoietic stem cell transplantation at two Bone Marrow Transplantation centers in Egypt from November 2016 to June 2017. Results: In our study, the patient male percentage was 57.1% in CMV reactivation group with the most common pre-transplantation diagnosis was FA, CML and βTM. All donors in the reactivation group (100 %) were positive for CMV IgG ab. This group had 42.9% matching donors in sex and blood groups. While the stem cell source was 92.9% peripheral blood source with a median dose of 7.0 cells ×10⁶ ∕ kg. Conclusion: The incidence of CMV infection following hematopoietic stem cell transplantation is comparable to that recorded in Western literature because of a higher seroprevalence rate in developing countries. More research is needed to study factors affecting cytomegalovirus reactivation in allogeneic hematopoietic stem cells transplantation (HSCT).