Background: Preterm birth, delivery prior to 37 completed weeks or 259 days gestation, is a worldwide maternal and perinatal challenge and is a leading cause of neonatal morbidity and mortality. Preterm birth remains the leading cause of perinatal and postnatal mortality and morbidity especially in developing countries where the health care services are suffering from limited resources. Premature babies usually suffer from both immediate and long term consequences. Right after birth, they have difficulties in breathing, temperature regulation, bleeding, infection and other problems due to organ immaturity. Their growth and developmental milestones will also be affected leading poor physical, mental, educational and psychosocial problems as a long term consequences. Preterm deliveries were responsible for 1 million out of the 6.3 million deaths of children under5 in2013 REF _Ref493689700 \r \h \* MERGEFORMAT [1]. In Kenyatta National hospital, few studies have been carried out to determine the prevalence and factors associated with preterm birth. Hence the aim of this study is to determine the prevalence and factors associated with preterm birth at Kenyatta national hospital (KNH), Nairobi, Kenya. Materials and Methods: This was a hospital based descriptive cross-sectional study involving randomly selected respondents (N = 183) from post natal ward of Kenyatta National Hospital. Systematic random sampling method was applied to recruit the study respondents. A pre-tested semi-structured questionnaire was employed to collect information on the possible determinants of Preterm birth. Data was analysed usingSPSSsoftware version 22.0. Descriptive analysis was done using mean and frequency proportion. Inferential analysis using chi-square test was used to establish association different variables. The ethical approval to conduct the study was obtained from KNH-University of Nairobi Ethical Review Committee (KNH-UoN ERC). Permission to collect data was sought from the KNH and consent was obtained from the selected respon