Gram negative bacteria (GNB) is the most common causative agent for morbidities and mortalities in leukemic patient, because of their receiving immunosuprresive chemotherapeutic agents, aggressive devices like catheters used for giving them those treatments and Hospitalization, in addition to GNB increasing resistance to many of antibiotics. The study include isolation of GNB from blood samples of leukemia patients and identification of GNB species isolated from those samples then testing its susceptibility to 15 antibiotics, moreover, calculating Procalcitonin (PCT) concentration in the samples as immunological marker to detect bacteremia in those patients. The results show presence of 9 GNB species in blood samples of leukemia patients including: Enterobacter cloacae, E. sakazakii, Serratia marcescens, S. ficaria, S. liquifaciens, S. rubideae, S. odorefera, Klebsiella oxytoca, and Pseudomonas fluorescens. The most common species was E. cloacae followed by E. sakazakii. The higher effective antibiotics were Ciprofloxacin, Gentamicin and Amikacin; also PCT concentrations were ranged between (0.1 and 8.23) ng.ml-1. The study concluded that Gram negative bacteremia was common causative agent for infections in Leukemia Patients, Enterobacteriacae was the the most common GNB causing infection, and the Most effective antibiotic for it were Ciprofloxacin, Gentamicin, and Amikacin which can be used as prophylactic therapies for those infections.