Background Infections contribute to 30% of the 2.5 million neonatal deaths that occur globally every year. A newly cut umbilical cord can be a pathway for bacteria to enter the vulnerable neonate and cause neonatal sepsis. Most infections are preventable with evidenced-based cord care. Objective To assess postnatal mothers’ knowledge and practice of umbilical cord care in the Kibungo Hospital catchment area in Rwanda.  Methodology A descriptive cross-sectional study design and purposive sampling strategy was used to recruit 224 postnatal mothers. Data were collected using a structured questionnaire. Descriptive and inferential statistics were used to analyze data.   Results A third of mothers (33%) had adequate knowledge, and a half (54%) had good umbilical cord care practice. The majority (70%) reported dry cord care practice, though many applied substances including Vaseline (23%) and Movit ointment (15%). There was a negative correlation between knowledge of cord care and substance applied to cord (R2=0.224, p=0.001), and days applied (R2=0.167, p=0.012).  Conclusion The study population had low cord care knowledge. Health care providers need to educate mothers on the practice of allowing the cord to dry naturally, and discourage the use of harmful substances that delay cord separation and increase risk of sepsis and subsequent neonatal mortality. Rwanda J Med Health Sci 2020;3(2):167-180