Bacterial infection continues to be the major cause of morbidity and mortality in the newborn of the developing countries. In Mongolia, 46% of deaths in neonates were due to sepsis in the period of 2004-2007. In Ulaanbaatar city 49.3% of late neonatal deaths were due to sepsis. Because the prognosis for sepsis largely depends on early identification and treatment, these neonates are subjected to extensive diagnostic evaluation and empirical systemic antibiotic treatment, pending laboratory results. Neonatal Sepsis is most likely to be caused by group B streptococci in developed countries and E. coli, Klebsiella sp. and Enterobacter sp. in developing countries. Methods. The present prospective study was performed in the neonatology unit of a tertiary-care Maternal and Child Health Resear Center after obtaining approval from the institutional ethics committee. Ninety seven neonates, ranging from birth to 30 days old, at risk of bacterial infection were evaluated. Risk factors were based on abnormal feto-maternal clinical findings, as described in standard textbooks of neonatology. One hundred and fifty two neonates with absence of feto-maternal risk factors were included in the present study as controls. This was to highlight the basic difference in the values of haematological parameters between neonates clinically suspected of infection and those who were without any risk factors. An extensive perinatal history, as well as a complete record of clinical signs and laboratory data, were recorded in each case. Blood samples were obtained from peripheral venipuncture in all neonates within 24 h of admission, before initiation of antibiotic therapy. Conclusions: 1. Most common risk factors of neonatal sepsis are maternal bacterial vaginosis (OR=5.7), kidney disease during pregnancy (OR=2.4), gestosis of pregnant women (OR=3.2), maternal infectious disease (OR=2.3), and anemia (OR=1.6). 2. Enterobacteriaceae was the most common organism isolated (55%), followed by Escherischia coli, and Klebsiella. 3. Among 73% of neonatest the clinical signs of sepsis were identified during the early neonatal period, 62% of them during the first 3 days of life. The common clinical type of neonatal sepsis was hypoergetic. 4. 60% of neonates were preterm and 44% were LBWI. 5. The haematological findings significantly associated with sepsis and their comparison with the values recommended. 6. A haematological score can be obtained by a complete blood count and examination of peripheral blood smear, thus permitting an objective assessment of haematological changes that occur in a neonate suspected of sepsis.