Background: Neonatal sepsis is a systemic inflammatory response syndrome in the presence of infection during the first 28 days of life. Globally every year about 4 million children die in the first 4 weeks of life, of which 99% of the deaths occur in low and middle income countries. In Ethiopia it is one of the most common causes of neonatal death. Identification of the determinants for neonatal sepsis is not adequate in low income countries like Ethiopia especially in southwest part of the country. Objective: The objective of this study was to identify determinants of neonatal sepsis among neonates admitted in neonatal intensive care unit at hospitals of Kafa zone, south west Ethiopia 2021. Methods: Institutional based unmatched case control study was conducted on a total sample of 248 (62 cases and 186 controls) in Hospitals of kafa zone from March 10 to April 20/2021. Neonates diagnosed as sepsis and admitted to neonatal intensive care unit were considered as cases and neonates diagnosed with other problem except sepsis were controls. For each case three controls were selected by lottery method. Data were collected through face to face interview with index mothers and neonatal record review checklist. The collected data were entered, coded and cleaned by Epidata version 3.1 and it was exported to Statistical Package for Social Sciences version 25. Bi-variable and multivariable logistic regression analysis was conducted. Variables with (p<0.25) in bi-variable logistic regression analysis, were entered to multivariable logistic regression and then determinants which is statistically significant were declared at P<0.05. Result: A total of 248 (62 cases and 186 controls) were included in the study. Among factors; rupture of membrane ≥18 hours [AOR=5.13, 95%CI=1.38-19.05], meconium stained amniotic fluid[AOR=6.03, 95%CI=2.16-16.90], intra-partum fever [AOR=8.26, 95%CI=3.12-21.97], urinary tract infections [AOR =14,55, 95%CI=4.91-43.10], breast feeding after a hour [AOR =3.9, 95%CI=1.27-12.02], resuscitation [AOR =13.25, 95%CI=3.44-51.01], no chlorohexidine application [AOR=4.27, 95%CI=1.65-11.08] were significantly associated with neonatal sepsis. Conclusion: According to this study both maternal (prolonged rupture of membrane, meconium stained amniotic fluid, fever, urinary tract infection, breast feeding) and neonatal factors (resuscitation, no chlorohexidine application) were independent determinants of neonatal sepsis. Therefore, preventive efforts of neonatal sepsis should emphasis on avoiding maternal risks and emphasis on high-risk neonates born from mothers who have prolonged rupture of membranes and urinary tract infection. Health professionals should advise early initiation of breast feeding and give appropriate newborn care. Key words: Kafa zone, neonatal sepsis, case control