Abstract : Neonatal sepsis is one of the major health problems throughout the world, the incidence of neonatal sepsis is 10 in 1000 live births, early diagnosis is complicated as early signs is minimal and similar to those of various non-infectious disease. Availability of laboratory tests provides accurate and rapid diagnosis of the disease would be of paramount importance in improving the outcome of this challenge problem. Procalcitonin PCT is one of calcitonin precursors, microbial infection result in ubiquitous increase in CALCI gene expression and subsequent release of calcitonin precursors from all tissue and all cell type throughout the body. It can be used a s a tool for diagnosis of bacterial disease in neonates and children . It can be detected in plasma 2 hours after injection of endotoxinTo assess the role of Procalcitonin as a marker in the early diagnosis, treatment and follow up of neonatal sepsis. The study carried out in NICU in Ahmed Maher Teaching Hospital including 3 groups (10 neonates in each group) , group 1 (proven sepsis) group 2 (suspected sepsis), group 3 (clinical sepsis) with total study size 30 neonates. Complete blood count, ESR, CRP, blood culture, Procalcitonin level, and other laboratory test as indicated were done at day 1 before start of treatment and day 5 after treatment. Data was analyzed using appropriate method. 66.6% had early onset sepsis, 33.4% late onset sepsis, Group I (proven sepsis) 5 cases were positive for E. Coli. 2 cases positive for staphyllococusaureus and 3 cases positive for Klebsiella. Procalcitonin level in 1st sample in group 1 (proven sepsis) was positive in 1 case and strong positive in 9 cases. In group 2 (suspected sepsis) 3 cases were negative, 5 cases were positive, and 2 strong positive. In group 3 (clinical sepsis) 3 cases were negative, 1 case was weak positive, and 6 cases were negative. While in 2nd sample (5 days after treatment), Group 1 (proven sepsis) 2 patients became negative and 8 became lower concentration, Group 2 (suspected sepsis) 8 patients became negative, Group 3 (clinical sepsis) all patient became negative Procalcitonin level is a useful marker in the early diagnosis and treatment and follow up of neonatal sepsis.