Allogeneic hematopoietic stem cell transplantation (allo-HSCT) is a potentially curative treatment for a variety of hematologic malignancies. Bacterial infections remain a common complication of allo-HSCT, especially in the pre-engraftment phase. Pre-engraftment neutropenia typically lasts for up to 2 weeks in autologous HSCT but is considerably longer in allogeneic HSCT recipients who receive myeloablative conditioning regimens. This is a prospective, randomized, controlled, phase II/III clinical trial that aims to investigate the beneficial and harmful effects of prophylactic use of imipenem in patients with hematological malignancies before allo-HSCT. All patients aged above 14 years, diagnosed with hematological malignancies and ready to undergo allo-HSCT, no active infection within 3 weeks before allo-HSCT, with a normal CT scan-chest before entering the transplantation cabin and willing to participate in the trial will be enrolled.